Support DC names containing spaces for replication jvm opts

[adejanovski]

Working on k8ssandra/cass-operator#362, it appeared that if DC names have spaces, there's no way to pass them in -Dcassandra.system_distributed_replication_dc_names without Cassandra's startup failing.
This is likely due to how Cassandra's startup script build the command line.

We need a workaround to allow such DC names to be supported by the -Dcassandra.system_distributed_replication_dc_names and -Dcassandra.system_distributed_replication  jvm options.