Write md5sum for service config directories

The configuration generated by docker-puppet may change on update,
so checksum the combined files from the config-data directories,
to enable detecting those that have changed and restarting the
appropriate containers - we need to merge this checksum into
the environment passed to the containters, as this will cause
paunch to correctly restart containers when the configuration
generated changes, even if the rest of the json definition
provided by heat does not.

Change-Id: I40d9080cf3ad708ef4ed91e46d2b2ae1138bb9c3