Running test-libmongoc --help outputs the names all of the tests by default, filling up the screen. We should hide printing out the test names in the help menu. E.g. only show the list of tests if a --list-tests flag is included test-libmongoc --help --list-tests.

Additionally the help menu prints to stderr. This is a minor annoyance if you want to search through the tests, since you can't pipe stdout directly into grep.