Minor fixes
Only clean dir if it exists in FileSourceModuleTests

If other initialization fails, we get an IllegalArgumentException
from the AfterClass method.
Fix possible overwriting of XD_TRANSPORT in tests

Attempt to fix problem in CI build where rabbit transport
is being used unexpectedly in stream integration tests which
should be using local transport but are loading rabbit files.
Add better test failure explanation
Update Spring, SI, MQTT Versions

- Spring 4.0.0.RC1
- SI, MQTT 4.0.0.M1