Add option to dsiable Cassandra's IPv4 stack preference.
Update cassandra-env.sh file from release.

Bump version to 1.2.4 and default config directory to the correct
one on the system.
Update MD5 hash for Cassandra package.
MERGING ALL THE THINGS

Merge branch 'master' into mm-cassandra-ipv6

Conflicts:
	ci_environment/cassandra/attributes/default.rb
Merge pull request #174 from travis-ci/mm-cassandra-ipv6

Add option to disable Cassandra's IPv4 stack preference.