SW-962: Replace head01 -> head in case of CEP4 headnode failover

Closes SW-962

See merge request !427

Resolve TMSS-691

Closes TMSS-691

See merge request !424

SW-961: Log stderr but do not use it as output to parse. Unfortunately, slurm...

Closes SW-961

See merge request !423

TMSS-728: Update JSON structure by moving SUBs outside durations

Closes TMSS-728

See merge request !419

Resolve TMSS-693

Closes TMSS-693

See merge request !418

Resolve TMSS-613

Closes TMSS-613

See merge request !417

TMSS-613: Beamformer SAP subbands issue solved. Added clear button in CustomDate component . Updated few messages.

Resolve TMSS-261

Closes TMSS-261

See merge request !409

SW-961: Log stderr but do not use it as output to parse. Unfortunately, slurm seems to give stderr output we occasionally have to ignore. If we need to ever check stderr, we may need a filter.

Resolve TMSS-725

Closes TMSS-725

See merge request !414

TMSS-725: processed review comment: split the ERROR state into (generic)ERROR and UNSCHEDULABLE which are both end-states.

TMSS-725: processed review comment. moved set_subtask_state_following_allowed_transitions into test_utils so that it is clearly intended to be used in tests only, and not in normal tmss code. Took the opportunity to move the TMSSTestEnvironment into its own module as well to make a clear distinction between test-helper-methods (in test_utils.py) and the TMSSTestEnvironment (in test_environment.py). Adapted all tests with new import paths.