Universal "reject" patterns

[mahavrila]

To consider and discuss:
check_output (in utils.py) allows user to specify reject patterns - if these patterns are present in output of tested command, exception is raised - our test Fails. Currently only a few of our tests have any reject pattern defined. It may be valuable to define "universal reject patterns" - for example "^.+failure". If the presence of "universal reject pattern" should cause Failure of the test or just Warning message would be defined based on future experience.

[mahavrila]

It may also help with logging of suspicious messages from output of tested commands.