Add new tape state REPACKING

We need a new tape state REPACKING to handle the queueing logic for tapes which are being repacked.

Currently we are using the DISABLED state for this. The DISABLED logic is as follows:

• It is not possible to queue on DISABLED tapes.
• The tape state can change to DISABLED after it has requests queued on it.
• Requests which end up queued on DISABLED tapes are re-queued by the maintenance process. However, as the maintenance process only attempts to requeue on the same tape, this effectively cancels/fails the request.
• There is a bug (see #1176 (closed)) that EOS is not notified when the request is cancelled.

The following tasks need to be done:

• Fix the bug mentioned above (#1176 (closed))
• Add the REPACKING state to CONSTRAINT TAPE_STATE_CK CHECK(TAPE_STATE IN ('ACTIVE', 'DISABLED', 'BROKEN')) in the DB schema
• Add the new REPACKING tape state to common::dataStructures::Tape
• Implement the logic of REPACKING as identical to the current logic for DISABLED described above
• Add commands to change the tape state to REPACKING to cta-admin
• Perform any necessary changes in the unit-test and system-tests, to cover for the new use-cases.

Once this is done, it will be possible to change the logic of DISABLED (#1170 (moved)), and the logic of REPACKING can be further refined (new tickets will be created for this as needed).