[CI] Fix our flaky test problems

[unlikelyzero]

We have quite a few instances of flaky tests affecting our PRs and causing unnecessary heartburn. This ticket captures some of the strategies available to be prioritized and executed during Build 5.

We have 3 categories of flaky tests:
A. Non-atomic. As of 07/26, when the tests are run in a random order, 3-8 tests fail.
B. Cross-talk or test isolation. When tests are run in a serially, certain tests fail 30% of the time. Possibly state leakage between tests or general memory leaks.
C. Browser/OS/Environment discrepancies. We're on rolling versions of node and chrome without a way to distinguish those changes vs legitimate PR failure.

Some solutions (more to come)

1. Run the circleci jobs every night to generate a baseline and watch for browser-specific regressions. Addresses C.
2. Hunt down memory leaks.
   1. Stackoverflow with a listing that plagued jasmine 1.x and 2.x.
   2. Worth checking this, too. Addresses B.
   3. Memory leak in Import/Export Plugin #4060
3. Create a nightly job which executes the tests in a random order. Addresses A.