Remove dependency on commons-lang.

Testing Done:
./gradlew clean build -Pq

Reviewed at https://reviews.apache.org/r/28021/
Drop argparse dependency; it's part of python 2.7

Testing Done:
./pants build src/test/python:all
bash src/test/sh/org/apache/aurora/e2e/test_end_to_end_v2.sh

Bugs closed: AURORA-891

Reviewed at https://reviews.apache.org/r/28140/
AURORA-933 - python missing license headers

Adds missing license headers to .py files

Bugs closed: AURORA-933

Reviewed at https://reviews.apache.org/r/28170/
Add more test coverage to SchedulerThriftInterface.

Bugs closed: AURORA-937

Reviewed at https://reviews.apache.org/r/28026/
Simplify Preemptor code, encapsulate parameters used there and in SchedulingFilter.

Reviewed at https://reviews.apache.org/r/28103/
Ensure all verbs return an exit code.

Bugs closed: AURORA-923

Reviewed at https://reviews.apache.org/r/27852/
Fix test_version to use explicit injection points.

Testing Done:
./pants src/test/python:all
./pants src/main/python/apache/aurora/client/bin:aurora_client
dist/aurora_client.pex version

Bugs closed: AURORA-938

Reviewed at https://reviews.apache.org/r/28250/
Fixing flaky LockManager test.

Bugs closed: AURORA-798

Reviewed at https://reviews.apache.org/r/28066/