Built a simple framework with a `dev/tests` directory to house all pull request related tests. I've moved the two original tests (`pr_merge_ability` and `pr_public_classes`) into the new `dev/tests` directory and tested to the best of my ability. At this point I need to test against Jenkins actually running the new `run-tests-jenkins` script to ensure things aren't broken down the path.

Author: Brennon York <brennon.york@capitalone.com>

Closes #5072 from brennonyork/SPARK-5313 and squashes the following commits:

8ae990c [Brennon York] added dev/run-tests back, removed echo
5db4ed4 [Brennon York] removed the git checkout
1b50050 [Brennon York] adding echos to see what jenkins is seeing
b823959 [Brennon York] removed run-tests to further test the public_classes pr test
2b9ce12 [Brennon York] added the dev/run-tests call back in
ffd49c0 [Brennon York] remove -c from bash as that was removing the trailing args
735d615 [Brennon York] removed the actual dev/run-tests command to further test jenkins
d579662 [Brennon York] Merge remote-tracking branch 'upstream/master' into SPARK-5313
aa48029 [Brennon York] removed echo lines for testing jenkins
24cd965 [Brennon York] added test output to check within jenkins to verify
3a38e73 [Brennon York] removed the temporary read
9c881ff [Brennon York] updated test suite
183b7ee [Brennon York] added documentation on how to create tests
0bc2efe [Brennon York] ensure each test starts on the current pr branch
1743378 [Brennon York] added tests in test suite
abd7430 [Brennon York] updated to include test suite