Here is a summary of failures for one particular task+variant: qa-tests-unstable on Ubuntu 1404:

• mongofiles_db.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/81ee2702f438e215dbac76f1595e1a92/test/5acd0972c2ab6808d040a408?bookmarks=0%2C2651%2C3500

• mongofiles_delete.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/f2f4de7c94030b1fc54a7e2bfcc87cf1/test/5acd0973be07c434193ac03b?bookmarks=0%2C3072%2C3921

• mongofiles_get.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/8aa49fafca441c9ce30e3a7a64c27a60/test/5acd0973be07c434193ac051?bookmarks=0%2C2742%2C3588

• mongofiles_host.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/ccd2da9f8d2ef8add4da6f158291fcd1/test/5acd097e90413046643a2534?bookmarks=0%2C2613%2C3462

• mongofiles_invalid.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/81ee2702f438e215dbac76f1595e1a92/test/5acd0bef90413046643a7df1?bookmarks=0%2C2425%2C3274

• mongofiles_list.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/f2f4de7c94030b1fc54a7e2bfcc87cf1/test/5acd0bf3c2ab6808d040fe3a?bookmarks=0%2C2724%2C3572

• mongofiles_local.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/8aa49fafca441c9ce30e3a7a64c27a60/test/5acd0bf490413046643a7eb2?bookmarks=0%2C2762%2C3611

• mongofiles_port.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/ccd2da9f8d2ef8add4da6f158291fcd1/test/5acd0c1cbe07c434193b201c?bookmarks=0%2C2584%2C3433

• mongofiles_prefix.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/81ee2702f438e215dbac76f1595e1a92/test/5acd0e6a54f248624d416cf5?bookmarks=0%2C2680%2C3528

• mongofiles_put.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/8aa49fafca441c9ce30e3a7a64c27a60/test/5acd0e6f54f248624d416dbc?bookmarks=0%2C3290%2C4139

• mongofiles_replace.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/f2f4de7c94030b1fc54a7e2bfcc87cf1/test/5acd0e70be07c434193b7e5d?bookmarks=0%2C2893%2C3742

• mongofiles_search.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/ccd2da9f8d2ef8add4da6f158291fcd1/test/5acd0ebac2ab6808d0416ccd?bookmarks=0%2C3498%2C4349

• mongofiles_type.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/81ee2702f438e215dbac76f1595e1a92/test/5acd10ccf84ae839d6650b20?bookmarks=0%2C2576%2C3424

• mongofiles_version.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/f2f4de7c94030b1fc54a7e2bfcc87cf1/test/5acd10ed54f248624d41bcde?bookmarks=0%2C2446%2C3294

• mongotop_sharded.js – server segfault
  https://logkeeper.mongodb.org/lobster/build/ccd2da9f8d2ef8add4da6f158291fcd1/test/5acd156190413046643c16f2?bookmarks=0%2C1547%2C2406

• oplog_rollover_test.js – Error: assert failed : mongodump --oplog should crash sensibly on oplog rollover
  https://logkeeper.mongodb.org/lobster/build/ccd2da9f8d2ef8add4da6f158291fcd1/test/5acd0957be07c434193abc42?bookmarks=0%2C151%2C174

• stat_discover_shard.js – --discover against a mongos sees all shards
  https://logkeeper.mongodb.org/lobster/build/81ee2702f438e215dbac76f1595e1a92/test/5acd1402f84ae839d665bc66?bookmarks=0%2C3403%2C3566

• stat_mixed_storage_engine.js – assert.soon failed, msg : discoverTest wait timed ou8t
  https://logkeeper.mongodb.org/lobster/build/f2f4de7c94030b1fc54a7e2bfcc87cf1/test/5acd1497f84ae839d665da81?bookmarks=0%2C4203%2C4392