Rj/refactor unit tests

[neontty]

major changes:

• tests are parallelizable now with xdist
• tests inherit from a base class that makes a copy of a repo for each one for isolated testing. cleans up tests on case exit
• tests all use a new repo that is outside of the current repo (publicly available HelloProphecy in prophecy-samples org)
• better coverage parity on most tests with the usage of pytest parameterization to check both scala/python

[neontty]

pytests are failing on github worker because spark sessions are crashing (likely due to OOM or something). runs fine on local machine.

need to try bottlenecking the tasks going to spark submit or just disabling parallel tasks

[neontty]

changes besides unittests:

1. 383 files changed but majority of that is because I deleted the entire resources directory which had the test projects. We now rely on external HelloProphecy project for testing
2. copy-paste refactor in pipeline.py that moved code for finding python dependencies into its own function
3. changes to regexes in prophecy_build_tool.py were to squash warnings for invalid escape characters. did not change regex functionality.
4. change to airflow.py is to catch a legitimate error found by unit tests
5. adding code to maven commands to allow for concurrent m2 cache access

[prongs]

minor: maybe we can make this a method in IsolatedRepoTestCase

[neontty]

good idea, will do

[neontty]

fixes #90 #96 #106