Bug 27839: Add tab-completion in bash for koha-worker

Bug 27839: Add tab-completion in bash for koha-worker

This patch simply adds tab-completion for this script.

To test:
1. Apply this patch
2. Run:
   $ cp debian/koha-common.bash-completion  /etc/bash_completion.d/koha-common
3. Open a new bash instance
4. Type 'koha-worker <tab>'
=> SUCCESS: All options are there
5. Play with Koha instances
=> SUCCESS: they show up, once chosen they are not offered anymore
6. Sign off :-D

Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>
Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>