vos: more details in vos release -verbose output

When running vos release with the -verbose flag, print the reasons for a
complete release, and the reasons for doing a full dump of the volume.  When
doing a full dump, have the verbose output print 'entire volume' instead of
'full release', to avoid confusion with a complete release.

Change-Id: I041da692bfea5d7eb0c96d51a5a794e3eeeb6d72
Reviewed-on: http://gerrit.openafs.org/9018
Reviewed-by: Mark Vitale <mvitale@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>