volinfo: accept -sizeonly for -sizeOnly

volinfo: accept -sizeonly for -sizeOnly

For consistency, allow -sizeonly (all lowercase letters) to
request the size summary. The old option name, -sizeOnly is
available as an alias.

Define the command line option parameter positions and use
those to set and look up the options.

Change-Id: Ie6a780e02bfa35cd5399364bab614b260c391abc
Reviewed-on: http://gerrit.openafs.org/4741
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>