Backport addCopySpecs() for rhel-6

A couple of recent backports to the nfs and openhpi plug-ins use
the addCopySpecs() API to collect multiple host files in a single
call.

Rather than adapt the plug-ins to make multiple calls backport
this trivial helper function to maintain as much consistency as
possible.

Signed-off-by: Bryn M. Reeves <bmr@redhat.com>