Reset subsystem state for integration tests.
Review Request #4219 - Created Sept. 10, 2016 and submitted
|jsirois, mateor, stuhood|
Some integration tests initialize a DistributionLocator (e.g., test_distribution_integration.py, test_shader_integration.py). They currently rely on the subsystem_instance() contextmanager to clean up that state, but that method is going away (because it can destroy state needed outside the context). This pre-cleanup helps prevent weird errors due to interactions between unrelated tests that happened to run in a certain order in a single process, typically on CI.
CI passes: https://travis-ci.org/pantsbuild/pants/builds/158967071