Allow running on unprivileged clusters

[zegelin]

Trying to run the operator/cassandra on an unprivileged cluster results in an error.

create Pod cassandra-test-cluster-cassandra-0 in StatefulSet cassandra-test-cluster-cassandra failed error: Pod "cassandra-test-cluster-cassandra-0" is invalid: spec.initContainers[0].securityContext.privileged: Forbidden: disallowed by cluster policy

Maybe we can make the init container optional?

[benbromhead]

We need to run a privileged container to configure certain OS options that will allow Cassandra to run in a reliable manner.

We can certainly make it optional, but it will make Cassandra more likely to break.

[alourie]

@zegelin following from #208, will work on this soon. Will restore the privelegedSupported functionality and whatever else will be needed here.

[alourie]

privilegedSuppored functionality is restored by #218