volinfo: refactor -sizeOnly printing

Refactor the -sizeOnly output processing to reduce code
duplication and coupling with -saveinodes.

Reviewed-on: http://gerrit.openafs.org/4732
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>

(cherry picked from commit 70145b4f4affc6aabf83fc1cc34cb4de0702c83f)

Change-Id: I8ca8979854959dc62ac5ff5147d2087e00e1f198
Reviewed-on: http://gerrit.openafs.org/11250
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams - CONTRACTOR <chas@cmf.nrl.navy.mil>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>