Update upstream URL for puppet-cassandra
Update upstream URL for puppet-cassandra

It has been transferred to Vox Pupuli [1].

Note that the pinned commit is a dummy commit to move release
to 999.999.999 which does not exist in the new repo so I'm also
updating the pin to the first commit in the new repo.

[1] https://github.com/locp/cassandra/blob/master/README.md

Change-Id: I00b055100c6670062c4ed4cfc51271a31b016dc8

redhat-openstack/rdoinfo,javierpena/rdoinfo