Runs in container

Tweak years in LICENSE file

Preroller: Don't allow initialization if either URI is missing

Revert Slave.WorkerPool changes; Clean up test issues

* Slave.WorkerPool: Revert a change to the `status` function that returned
  cached async responses rather than making an RPC request. The change broke
  tests that relied on seeing changes immediately, and the function isn't
  used elsewhere.
* util/IcecastSource: Clean up a case where our callback could be fired twice
* tests/slave: Update slave status response expectations