SW-828: abstracted RADBCommonTestMixin into even more common PostgresTestMixin. adapted t_postgres.py and radb_common_testing.py to new PostgresTestMixin.

SW-816: improved speed of the RADBCommonTestMixin by only creating a postgres instance upon setUpClass, and applying a fresh radb schema every test via setUp

SW-816: bonus feature: refactored RADBCommonTest into a RADBCommonTestMixin which takes care of setting up a testing postgres radb instance, and which can be used in conjunction with a unittest.TestCase to do unittests on a fresh RADB instance. By using a mixin instead of chained inheritance we have better seperation of responsibility, and tools like pycharm can handle these tests better as well.

Resolve SW-796

See merge request !26

(cherry picked from commit ae8f2617)

fe65ce37 SW-796: fixed radb tests
65b4d86f SW-796: fixed t_momqueryservice.py. We still need to un-skip IntegrationTestMoMDatabaseWrapper.
389ea3e4 SW-796: fixed tpyparameterset
4e44e3c3 SW-796: fixed t_TreeStatusEvents
63b9b189 SW-796: typos
2eb326cc SW-796: fixed ingest typos and tests
be63b190 SW-796: fixed t_qa_service
764d8d76 SW-796: fixed t_qa_service
17478140 SW-796: fixed (not-so-complete) test_ra_service_and_rpc
67306896 SW-796: fixed tRATaskSpecified
469fe393 SW-796: fixed t_resource_estimator
6d87ea88 SW-796: fixed t_schedulechecker
3fba3ba2 SW-796: fixed t_resource_availability_checker
7b1f0f7b SW-796: fixed typos in scraper.
c5dc773e SW-796: fixed t_resourceassigner
7f165dd2 SW-796: fixed t_resourceassigner
de48d55c SW-796: fixed ltastorageoverview tests: test_store, integration_test_store and test_lso_webservice
977ee079 SW-796: fixed t_schedulers
6d691753 SW-796: Merge branch 'SW-796' of git.astron.nl:ro/lofar into SW-796
ca84122f SW-796: fixed tresourcetool
98cc4a38 SW-796: fixed t_translation_service
4150a16d SW-796: fixed t_specification_service
c9a5988b SW-796: fixed t_TriggerEmailService
4e779152 SW-796: fixed t_trigger_service
60e265b9 SW-796: fixed t_trigger_cancellation_service
897bd380 SW-796: fixed build dependency for t_ingestpipeline
469e29cd SW-796: Set default port to the one in production.
2c551559 SW-795: Change timeout because its too short for the tests running on the buildhost.
47a70ce8 SW-795: Change timeout to match tested timeout

This includes:
- python executable -> python3
- Help texts
- #! specifications
- Shell scripts