Bug 14714: Add tab-completion to koha-mysql command

Bug 14714: Add tab-completion to koha-mysql command

This patch introduces tab-completion in bash to the koha-mysql
command. It completes using valid instance names. It stops completing
once an instance name is chosen (i.e. it respects the fact that
koha-mysql accepts only one instance name as parameter).

To test:
- Have a packages install (kohadevbox works)
- Run:
  $ . debian/koha-common.bash-completion
- Type
  koha-mysql <tab>
=> SUCCESS: You are prompted valid instance names for completion.
- Sign off :-D

Signed-off-by: Nick Clemens <nick@quecheelibrary.org>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>