Preserve exclusive activation of cluster mirror when converting.

Preserve exclusive activation of cluster mirror when converting.

This patch to the suspend code - like the similar change for resume -
queries the lock mode of a cluster volume and records whether it is active
exclusively.  This is necessary for suspend due to the possibility of
preloading targets.  Failure to check to exclusivity causes the cluster target
of an exclusively activated mirror to be used when converting - rather than
the single machine target.