volinfo: refactor volume and vnode handling code

Refactor volume and vnode handling code for better
maintainability.  Move the code invoked by -saveinodes to a new
function. Remove an unneeded else clause in HandleVolumes.

Reviewed-on: http://gerrit.openafs.org/4734
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 56714e9a4d01d1718bbca9f3930c2993e4b7d094)

Change-Id: I96da8a2824af7283fa2d3fb34622d06715c058cb
Reviewed-on: http://gerrit.openafs.org/11252
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>