Avoid filtering tests if testClassRegexes entry is not set in Marathonfile

[alex-apriamashvili]

Currently, there is a filtering logic in place to filter-out irrelevant test-cases received from the test-case parser. However, we might not need to filter any of those test-cases found at all! For example, all the cases found by IOSTestParser might be used for testing which makes that parameter redundant in some situations. However, shall the testClassRegexes not be specified, all the tests provided by a parser will be filtered out. This situation could be solved by simply specifying the following inside the Marathonfile:

testClassRegexes:
- "^.*$"

But why to specify this parameter at all if it could be avoided?

I suggest skipping the filtering step for the cases when the testClassRegexes is not specified in Marathonfile.

P.S: I don't mind making this change myself.