cmd: Add accessor functions for options

cmd: Add accessor functions for options

Add a load of accessor functions to help with pulling values out
from the the cmd_syndesc structure. The idea here is to make it
simpler to manipulate command line values, as well as starting to
hide the structure of the cmd_syndesc structure from callers, with
a view to eventually making it private to the cmd library.

Change-Id: I38757d776364ceacd43e98fda16e995da35da65c
Reviewed-on: http://gerrit.openafs.org/4543
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>