XD-1838 FileSourceTest applies uses labels

* SimpleFileSource & SimpleFileSink supports labels.
* Type parameter restriction in AbstractModuleFixture to allow methods to
  return subclass type.
* Create getDslLabel utility method to create start of the DSL with a label.
* Minor formatting changes
XD-1850: IllegalStateException when deploying orphaned...

XD-1850: IllegalStateException when deploying orphaned stream
modules upon a matching container arrival

This was caused by a modification in StreamDeploymentsPath that
now requires module type, module label, and container to be
present since these three fields have been combined into a
single node (see XD-1591).
XD-1851 Introduce cache to ZooKeeperContainerRepository

Introduced PathChildrenCache to ZooKeeperContainerRepository
to address the concerns indicated in
https://github.com/spring-projects/spring-xd/pull/936

Container cache no longer needs to be a member

Since the container cache is no longer externally accessible
due to ZooKeeperContainerRepository, this was moved
to be a local variable within the leader election method.
XD-1775 & XD-1781 HdfsJdbc, HdfsMongo Accept Tests

* Address comments in PR review https://github.com/spring-projects/spring-xd/pull/914/
XD-1814 Acceptance Tests for Labels and Taps

* Includes Transform fixture as well.
* Improvements to Result File Validator.
** The file validator now checks to see if the file is present and loops
   for a period of time with one second pauses if not present.
   Before we always waited pausetime *2000 (millis).
** Runtimes were about 17 min with the latest checks.  Now they are
   running around 12 min.
* testStreamTapTwoProcessors Uses labels vs. module index.
* Delimiter now spelled correctly
* Thread.currentThread().interrupt() is now in the catch block for the thread.sleep
* Removed code for index that was no longer relevant.
XD-1760 Rabbit/Redis Bus Short Circuiting

For colocated modules, when instructed by the lead admin,
hard wire the modules together.

- When binding a short-circuited producer, save his properties in
the binding so they can be used to revert, when the consumer is
unbound.

- When the consumer is unbound, bind the producer to the bus
(concurrently with the direct binding), remove the direct binding,
then stop the consumer (so there is always at least one subscriber
to the producing module's output channel.

- If the consumer is re-deployed, switch back to short circuit.

- TODO: Currently requires a producer property `shortCircuitAllowed`