Bug 24340: allow koha-sip --disable inst

Bug 24340: allow koha-sip --disable inst

To test:

- Enable sip for your testing instance
 sudo koha-sip --enable inst
- Start sip for your testing instance
 sudo koha-sip --start inst
- Verify it is running
 ps ax |grep sip -> you should see processes
- Disable sip for your testing intance
 sudo koha-sip --disable inst
- Verify that the following has happened:
 * SIP is no longer running for your instance - no SIP processes
 * SIP Cannot be started for the instance because it is not enabled.

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>