Bug 13791: tab-completion for koha-plack in bash

Bug 13791: tab-completion for koha-plack in bash

This patch adds tab-completion in bash for the koha-plack command.

After the --start, --stop, --restart and --disable switches it only offers
plack-enabled instances.  And disabled instances to --enable.

--help and -h just finish end the completion.

--quiet and -q are trickier to implement. They will work (be offered)
only before the action switches.

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Tomas Cohen Arazi <tomascohen@unc.edu.ar>