Allow resmoke.py to filter tests by function name in test file

resmoke's test filtering currently operates on a file level. But for unit tests and benchmark tests, there is usually more than one test per file. They support the --filter and --benchmark_filter respectively to run specific functions in a file. We could add an option to resmoke to support these options, maybe as another phase in the selector on top of the existing file-based selection.

Some JS tests also have more than one "test" per file, so it might be interesting to pipe this logic to JS files as well.