Improve system_tests
Update documnetation
One more refactoring of system_tests
Fix cluster creation in HA mode. Removed unused update cluster mode function
Package for integration tests
Move thread-related tests to 'integration'
Remove unused imports
Create runner for integration tests.
Fail tests on exceptions in threads
Create requirements-test-eggs.txt
Update test requirements
Update base test classes
Move some tests to integration
Implement TestClusterValidator
Fix typo
Implement TestAttributesValidator
Implement TestRedHatAccountValidator
Update Red Hat handler tests
Merge with master
Separate unit and integration tests
Fix flake8 violations