Create and use constants for landing zone status types

[gromdimon]

Issue #1398

TODO:

• Implement
• Test

[mikkonie]

Looking good! I can see two issues:

Issue 1

Importing large amounts of these constants in modules can bloat up the import sections quite a bit. I suggest you move these and the other landingzones constants into landingzones/constants.py. Then, if you need a big bunch of these constants imported in a single module, you can instead do:

import landingzones.constants as lc
do_something_with(lc.ZONE_STATUS_OK)  # Etc etc.

Issue 2

Grep shows me there are still places where we refer to these status types by string instead of the constant. Mostly in tests but also elsewhere. Example:

(sodar14) mikkopen@cubi-7300-mn:~/code/sodar$ grep -niIr --include "*.py" "'MOVED'"
samplesheets/views.py:1358:                    status__in=['MOVED', 'DELETED']
landingzones/management/commands/inactivezones.py:23:    ).exclude(status__in=('DELETED', 'MOVED'))
landingzones/plugins.py:128:        if obj.__class__ == LandingZone and obj.status != 'MOVED':
landingzones/plugins.py:169:        active_count = zones.exclude(status__in=['MOVED', 'DELETED']).count()
landingzones/models.py:24:ZONE_STATUS_MOVED = 'MOVED'
landingzones/models.py:75:STATUS_FINISHED = ['MOVED', 'NOT CREATED', 'DELETED']
irodsadmin/management/commands/irodsorphans.py:87:            ~(Q(status='MOVED') & Q(status='DELETED'))
taskflowbackend/tests/test_flows.py:632:        self.assertEqual(self.zone.status, 'MOVED')
taskflowbackend/tests/test_flows.py:691:        self.assertEqual(self.zone.status, 'MOVED')
taskflowbackend/tests/test_flows.py:763:        self.assertEqual(self.zone.status, 'MOVED')
taskflowbackend/tests/test_flows.py:967:        self.assertEqual(new_zone.status, 'MOVED')
taskflowbackend/flows/landing_zone_move.py:329:                    'status': 'MOVED',

We should consistently use the constants everywhere.

[mikkonie]

No notes, good work! Will be merged :)