Create a pytest plugin for random bugs

The current implementation of RandomBug is not well done. For instance, the "STRICT" mode does not work.
As we are using pytest, we should create a plugin that does this one thing the right way.

The annotation could be:

@pytest.mark.random('Reason, ticket, ... ', **kwargs)
def test_foo():
    pass

Where possible arguments are:

• condition (bool): the condition to use the random, if False run the test normally. Default is True.
• repeat (int): how many times should we repeat the test. Default is 10.
• mode (str):
  • "RELAX": will retry as repeat times until it succeeds. Default value.
  • "STRICT": will repeat it until it fails or hits the repeat limit.
  • "BYPASS": skip the test.

Also, it should be possible to set the mode from the envar RANDOM_BUG_MODE.