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
Fix Swift config dir variable name

Change SWIFT_CONFIG_DIR to SWIFT_CONF_DIR to be consistent with all other projects.

Change-Id: I52b7d08f038c28a16caa669d7d1aa5248fbe7789
Merge "Fix Swift config dir variable name"