Adding Read-Only volume attaching support to Cinder client

Adding mode argument to volume manager attach function.
Allow Nova using read-write or read-only mode to attach a volume to an
instance.

blueprint read-only-volumes

Change-Id: Ib20c7802304d83f4aafef522171ebd47f672d883
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Adding volume readonly-mode-update interface to Cinder client

Adding volume readonly-mode-update interface to shell and client object
(v1 and v2) to allow end user update volume read-only access mode flag.

blueprint read-only-volumes

Related-Id: I4c84614d6541d5f7c358abadb957da7b8c3d9c48
Change-Id: I2d587f301a21c0d42b8940465862da25a70ed5a8
Signed-off-by: Zhi Yan Liu <zhiyanl@cn.ibm.com>
Merge "Adding volume readonly-mode-update interface to Cinder client"