viced: Add options for interrupting clients

Add the -offline-timeout and -offline-shutdown-timeout options to the
fileserver, to implement interrupting clients accessing volumes we are
trying to take the volume offline. Document the new options.

Currently this is only implemented for read operations. Implementing
this for write operations and callback breaks will require more work.

This also removes the VGetVolumeTimed interface from the volume
package, since the fileserver was the only user and with this change
the fileserver now uses the VGetVolumeWithCall interface.

Reviewed-on: http://gerrit.openafs.org/2984
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 4f7a51aa5115a9073771bc396e25d510aeae71e8)

Change-Id: I34967bb03a09e5655b02c9b7b39272cfe8f71d7b
Reviewed-on: http://gerrit.openafs.org/10799
Reviewed-by: D Brashear <shadow@your-file-system.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>