sanitizer-bootstrap bot: make ubsan failures non-fatal

Someone needs to do a cleanup and re-enable; until then
"check-llvm ubsan" and "check-clang ubsan" will stay orange but
the bot in general will be green, so we would at least catch
regressions in the other testing modes.


git-svn-id: https://llvm.org/svn/llvm-project/zorg/trunk@222914 91177308-0d34-0410-b5e6-96231b3b80d8