restore ability to pass multiple jobs on 'update'

4f5cfb17 gave us the ability to pass multiple job names when running the
`update` command.  Unfortunately the argument parser was made to request
at least one argument.  a0ccb45c fixed it to be one optional argument
which in turn broke the ability to pass several jobs.

This patch makes the names argument to consume all remaining arguments
and not require any.

Change-Id: I4723117d607f7e10223985fdcbdd50fc5ca50183
Reviewed-on: https://review.openstack.org/24711
Reviewed-by: will soula <william.soula@drillinginfo.com>
Reviewed-by: Khai Do <zaro0508@gmail.com>
Reviewed-by: Antoine Musso <hashar@free.fr>
Reviewed-by: James E. Blair <corvus@inaugust.com>
Approved: Jeremy Stanley <fungi@yuggoth.org>
Reviewed-by: Jeremy Stanley <fungi@yuggoth.org>
Tested-by: Jenkins