Merge remote-tracking branch 'upstream/master'
Removed unnecessary imports from aggregate_tests.py.
Rewrote extraneous dependencies test, based on arbitrary package test.
Aggregate tests now passes. Moved various unit test code that ran on import into setup and teardown functions that are called at the appropriate time when run with other tests.
Removed stray debug code.
Make aggregate tests randomization optional.
Review Zane's unit test fixes and resolve merge conflicts
Review Zane's unit test fixes and resolve merge conflicts
Merge branch 'zanefisher-fix_tests' into develop
Merge branch 'develop' into refactor-download-update

Conflicts:
	tuf/tests/aggregate_tests.py
	tuf/tests/test_signercli.py
	tuf/tests/test_signerlib.py
	tuf/tests/test_updater.py