XD-1672 filepollhdfs Acceptance Test

* Hdfs based tests will use assertValidHdfs
* Remove overloaded SimpleFileSink.toDSL method
* Replaced FileSourceTest's triggers with http
XD-1747: Module deployment order is not guaranteed

Modified writeDeployment to deploy each module serially (but still
write out deployment requests for a module to multiple containers
at once). This is required to guarantee that modules for a stream
are deployed in the correct order.