CassandraDatacenter CRD needs to be installed for integration tests

[jsanda]

The integration tests in #6 are failing with this error:

2020-11-19T13:30:18.023-0500	ERROR	controllers.Reaper	failed to check for CassandraDatacenter readiness	{"reaper": "reaper-test-0/test-reaper", "error": "CassandraDatacenter.cassandra.datastax.com \"test-dc\" not found"}

After some investigation, we discovered that this is due to not installing the CassandraDatacenter CRD. This is breaking integration tests.

I think we need to properly kustomize cass-operator because this will be needed for medusa-operator as well. I think that should be addressed separately but wanted to point it out.