Unify guestfish and guestmount options processing (RHBZ#642932).

Unify guestfish and guestmount options processing (RHBZ#642932).

In guestfish, factor out the processing of the options -a, -c,
-d, -i, -m, -n, -r, -v, -V, -x into a separate set of files:
options.c, options.h, inspect.c, virt.c.

Change guestmount so that it uses these same files (from the
../fish directory) to process the same options.

This unifies the handling of these options between the two programs.
It also adds the useful inspection feature to guestmount, so you
can now do:

  guestmount -d Guest -i --ro mnt/