Allow signalTransport option for sw deployments

Defaults to null (which in turn will cause heat to use its
default) but allows control over software deployment signalling,
in particular to use 'NO_SIGNAL' if required not to wait for success
or failure.

Change-Id: I7b8bb553724173261d9475e2d574fc0e413d2b3e
Merge "Allow signalTransport option for sw deployments"