Add a parameter to the current E2E tests that, if set, will execute the UI test at the end.

The UI tests should run in the same pipeline step, right after the E2E test suite succeeds. 

• add a command to run UI tests right after the E2E test suite
• don't overwrite the already existing artifacts (should be done by https://issues.redhat.com/browse/RHTAPUI-82 )
• export important env vars (as component name) from E2E tests and use them in the UI suite