Add clean.sh

clean.sh gets rid of all residue of running DevStack except installed
packages and pip modules.

And it eradicates rabbitmq-server and ts erlang dependencies as well as
the other RPC backends and databases.

Change-Id: I2b9a251a0a151c012bae85a5a2f9c2f72e7700be
Merge branch 'run-service' into dt-test
Merge branch 'swift-conf' into dt-test
Merge branch 'clean-me' into dt-test