Setup, teardown, DEBUG=core, FAILFAST fixes

Setup, teardown, DEBUG=core, FAILFAST fixes

- Fixed a bug when an error occuring in tearDownClass would not result in
test being marked as failed
- Improved test results reporting in cases when an error occurs in setUpClass
and tearDownClass
- Fixed DEBUG=core when the core is produced in setUpClass or
tearDownClass
- Reworked DEBUG=core to always be handled after all tests have been
executed
- Fixed FAILFAST=1 for parallel test runs

Change-Id: I3e9cd3b97ba6fa802fa0aa2dd7678ff82eee09ec
Signed-off-by: juraj.linkes <juraj.linkes@pantheon.tech>