EGLThreadTest doesn't clean up well and the test framework can't handle
it well. It caused test failures related to eglMakeCurrent (ELG_BAD_ACCESS)
on Android that were masked by retries.

Calling eglGetDisplay within a test can cause it to return a cached
display from the test runner.  The test is unable to know if it should
terminate this display.

bug: angleproject:3321
Change-Id: I14a539a00acaed4ee71622e7416a6c7a75596606
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1541717
Commit-Queue: Jonah Ryan-Davis <jonahr@google.com>
Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jamie Madill <jmadill@chromium.org>