volinfo: refactor mode variables

volinfo: refactor mode variables

Untangle the various global mode variables, which became muddled when dsizeOnly
and saveinodes were introduced. DumpInfo now indicates the default mode and
DumpVnodes means print the vnode entries, not scan but sometimes print.  Remove
unused globals.

Change-Id: I9d331a19afede864ad1d23477f5e3948e59558ec
Reviewed-on: http://gerrit.openafs.org/4735
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>