Add functions:
* SetMirrorMode implementing rbd_mirror_mode_set
* GetMirrorMode implementing rbd_mirror_mode_get
* MirrorEnable implementing rbd_mirror_image_enable2
* MirrorDisable implementing rbd_mirror_image_disable
* MirrorPromote implementing rbd_mirror_image_promote
* MirrorDemote implementing rbd_mirror_image_demote
* MirrorResync implementing rbd_mirror_image_resync
* MirrorInstanceId implementing rbd_mirror_image_get_instance_id
For now, these mirroring related functions are only supported on octopus
builds. Right now the demand is for snapshot based mirroring, which is
new in octopus. We can always relax this in the future and add the
necessary support for nautilus, for journaling only based mirroring.
Signed-off-by: John Mulligan <jmulligan@redhat.com>