Dispose session in cascade tests

[bahusoid]

Not sure why MergeDeliveryNodeAsync is unstable on appveyor. But at least fail shouldn't lead to lock in db.

Test exception stacktrace just in case

System.Collections.Generic.KeyNotFoundException : The given key was not present in the dictionary.
[00:08:22]    at System.ThrowHelper.ThrowKeyNotFoundException()
[00:08:22]    at System.Collections.Generic.Dictionary`2.get_Item(TKey key)
[00:08:22]    at NHibernate.Engine.StatefulPersistenceContext.ReplaceDelayedEntityIdentityInsertKeys(EntityKey oldKey, Object generatedId) in C:\projects\nhibernate-core\src\NHibernate\Engine\StatefulPersistenceContext.cs:line 1356
[00:08:22]    at NHibernate.Action.EntityIdentityInsertAction.d__18.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Action\EntityIdentityInsertAction.cs:line 73
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Action.EntityIdentityInsertAction.d__17.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Action\EntityIdentityInsertAction.cs:line 63
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Engine.ActionQueue.d__3.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Engine\ActionQueue.cs:line 74
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Engine.ActionQueue.d__0.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Engine\ActionQueue.cs:line 35
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Engine.ActionQueue.d__5.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Engine\ActionQueue.cs:line 108
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at NHibernate.Engine.ActionQueue.d__5.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Engine\ActionQueue.cs:line 117
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Event.Default.AbstractFlushingEventListener.d__6.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Event\Default\AbstractFlushingEventListener.cs:line 255
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Event.Default.DefaultFlushEventListener.d__0.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Event\Default\DefaultFlushEventListener.cs:line 28
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Impl.SessionImpl.d__64.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Impl\SessionImpl.cs:line 1005
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Impl.SessionImpl.d__77.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Impl\SessionImpl.cs:line 1248
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Transaction.AdoTransaction.d__1.MoveNext() in C:\projects\nhibernate-core\src\NHibernate\Async\Transaction\AdoTransaction.cs:line 59
[00:08:22] --- End of stack trace from previous location where exception was thrown ---
[00:08:22]    at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw()
[00:08:22]    at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
[00:08:22]    at NHibernate.Test.Cascade.Circle.MultiPathCircleCascadeTestAsync.d__11.MoveNext() in C:\projects\nhibernate-core\src\NHibernate.Test\Async\Cascade\Circle\MultiPathCircleCascadeTest.cs:line 228