Add heapdump to dev dependencies

Including it by default makes it easier to take a heap dump in production (by
sending SIGUSR2) without a need to manually install it there.
Search Cassandra for local/test keyspaces to drop

Conflicts:
	test/util/cleandb.sh
Merge pull request #81 from gwicke/master

Misc tweaks
Merge pull request #82 from wikimedia/smart-clean

Search Cassandra for local/test keyspaces to drop