index_bigkeys_nofail.js triggers spurious failures when run in parallel with other tests

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:

• https://evergreen.mongodb.com/task/mongodb_mongo_v3.0_ubuntu1204_parallel_eb79bd1fe807512e54c68c5982b2a24fa1d66bba_15_12_16_20_38_13
• https://evergreen.mongodb.com/task/mongodb_mongo_v3.0_rhel55_parallel_eb79bd1fe807512e54c68c5982b2a24fa1d66bba_15_12_16_20_38_13