ubuntu 14.04 tests support

Latest changes to teuthology may prevent tests to be able to run on ubuntu 14.04 ref: https://github.com/ceph/teuthology/commit/629f343dde18c2fad371bca0963b731c6e... https://github.com/ceph/teuthology/pull/1294#issuecomment-500568491 (Zack and David have more on why) There are some tests that have ubuntu 14.04 configurations specified ATM. Question - is it OK to remove references from those suites ? Do we have any use cases when ubuntu 14.04 must be supported? Thx YuriW