Add Mesos formula

Builds on #24105 and updates it to the current Mesos release (0.19.0).
Mesos compiles on clang since a few versions ago so I removed the compiler checks.
@mikemcquaid I looked at some formulas that are also daemons - [Cassandra](https://github.com/Homebrew/homebrew/blob/master/Library/Formula/cassandra.rb) and [Zookeeper](https://github.com/Homebrew/homebrew/blob/master/Library/Formula/zookeeper.rb) and neither of them have tests. I assume because of similar issues. Since the formula works, would you merge it? I'm happy to add the test later if I get some guidance.