Fix secret lookup_by_usage.
Fix secret lookup_by_usage.

The argument parsing was completely bogus before, so nothing
would work.  This is now fixed and seems to work fine.

Signed-off-by: Chris Lalancette <60b62644009db6b194cc0445b64e9b27bb26433a@redhat.com>

klynch/ruby-libvirt,klynch/ruby-libvirt,klynch/ruby-libvirt