vol: Add VGetVolumeTimed

vol: Add VGetVolumeTimed

Replace the VGetVolumeNoWait interface with the more general
VGetVolumeTimed interface, which allows for waiting for offlining
volume for arbitrary amounts of time (instead of just "waiting
forever" or "not waiting at all"). Also add VOL_CV_TIMEDWAIT and
VTimedWaitStateChange_r as necessary to implement this.

Change-Id: I3d9ea7a89f16ec5fd185eae7679e84033eb2d581
Reviewed-on: http://gerrit.openafs.org/3214
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>