CBQE-2296: api to manage cluster_run nodes

provides an interface to ns_server cluster_run cli when run within couchbase repo.

usage:

    crm = CRManager(num_nodes, start_index)
    rc = crm.start_nodes()
    rc = crm.stop_nodes()

Change-Id: I7485e325fbd0f0a851d409d5669f8544bbc90fd4
Reviewed-on: http://review.couchbase.org/38696
Tested-by: Tommie McAfee <tommie@couchbase.com>
Reviewed-by: Tommie McAfee <tommie@couchbase.com>