The index_bigkeys_nofail.js test toggles the failIndexKeyTooLong failpoint, which can cause the index_bigkeys.js test to fail because an index will actually be created even when the index key length is exceeded.
A change was already committed to skip running the index_bigkeys_nofail.js test in parallel with other tests: https://github.com/mongodb/mongo/commit/a66cc2118c711caf28a823be7c79cbf1b5c0942c. The purpose of this ticket is to track backporting that change to the 3.0 branch.
Recent failures on the 3.0 branch: