Allow logging warnings or errors on unit tests

[baturayo]

Unit tests using tests.helpers.scanner.Scanner object fails by default if there is a warning or error in the logs. It is due to the assert_no_error_nor_warning_logs method.

For some unit tests, we need to have warnings. For example, automated monitoring test raises a warning message that "Automated monitoring is not implemented yet!.." but due to this message the unit test fails.

By default, we can raise an AssertionError if there is an error or warning log but for some exceptional cases like automated monitoring, we can have an argument in the tests.helpers.scanner.Scanner class that does not fail in case of warnings or errors.

CC: @bastienboutonnet @tombaeyens @vijaykiran

[jmarien]

SODA-262