Don't require a test path when running with --test

Before:

```
krall@dev1-devb:~/pg/Testify () $ testify --rerun-test-file=test_list.txt
Usage: testify <test path> [options]

testify: error: Test path required unless --connect specified.
```

After:

```
krall@dev1-devb:~/pg/Testify (no_filename_when_rerunning) $ testify --rerun-test-file=test_list.txt
.
PASSED.  1 test / 1 case: 1 passed, 0 failed.  (Total test time 0.00s)
```