util: add method to get rados connection
util: add method to get rados connection

New go-ceph admin package api's expects to
pass the rados connection as argument.
added new method called GetRBDAdmin
to get admin connection to administrate
rbd volumes.

Signed-off-by: Madhu Rajanna <60fbf37a92c2a0908e31296d18dadbec5a4dae17@gmail.com>

ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi,ceph/ceph-csi