Improve the D-Bus monitor script

[mulkieran]

It should self-monitor to verify that it has stopped receiving signals before it stops. We could possibly simplify the wait actions in the post-test check that invokes the script and that could end up shortening the total run time of the whole thing.

[mulkieran]

The idea is that after the KeyboardException is picked up the script will loop waiting for additional signals and will not actually do the comparison until it stops getting the signals from stratisd.