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.

Reviewed-on: http://gerrit.openafs.org/3214
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
(cherry picked from commit db6ee95864a8fc5f33b7e95c19c8ff5058d37e92)

Change-Id: I6c7b3a0b9fe174ebffeb03153dda1c4705d7dac5
Reviewed-on: http://gerrit.openafs.org/6264
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>