SERVER-22349 Throw interruptions from loadStored

The JS engine's loadStored eats exceptions that occur while it's loading
functions from system.js.  This also eats interruption exceptions, which
can lead to a situation where a map reduce job is killed during
loadStored, but the interrupt is lost. For tests where the map or reduce
stages are long or non-terminating, and we rely on killing them, this
can lead to hangs.

Re-throwing interrupts from the try/catch block around loadStored fixes
this behavior.

Author: hanumantmk

src/mongo/scripting/engine.cpp

@@ -231,6 +231,10 @@ void Scope::loadStored(OperationContext* txn, bool ignoreNotConnected) {
             thisTime.insert(n.valuestr());
             _storedNames.insert(n.valuestr());
         } catch (const DBException& setElemEx) {
+            if (setElemEx.getCode() == ErrorCodes::Interrupted) {
+                throw;
+            }
+
             error() << "unable to load stored JavaScript function " << n.valuestr()
                     << "(): " << setElemEx.what() << endl;
         }

src/mongo/scripting/mozjs/implscope.cpp

@@ -185,7 +185,7 @@ bool MozJSImplScope::_interruptCallback(JSContext* cx) {
     if (scope->_hasOutOfMemoryException) {
         scope->_status = Status(ErrorCodes::JSInterpreterFailure, "Out of memory");
     } else if (scope->isKillPending()) {
-        scope->_status = Status(ErrorCodes::JSInterpreterFailure, "Interrupted by the host");
+        scope->_status = Status(ErrorCodes::Interrupted, "Interrupted by the host");
     }
 
     if (!scope->_status.isOK()) {