Added flexible publish support

Added support for the Flexible Publish plugin to the JJB publishers.
Updated documentation and unit tests as well.

Change-Id: Id72a4b01f451ae2613b24347afb6493bf7641cd1
Add tests for properties inject

Replace hard-coded inject example with a literal include. Extend the
example to show how to pass two environment variables.

Add test fixtures for the keep-system-variables and keep-build-variables
parameters.

Change-Id: Ie3b5af2c38f8dde5ff739b9f6b213c1e94387aca
Add support for "Override Build Parameters" option in EnvInject

Change-Id: I4f0c9949f1141ccf93ea86d6cdaec6cce7e6ac4d
Merge "Add tests for properties inject"
Merge "Add support for "Override Build Parameters" option in EnvInject"
Merge "Added flexible publish support"