Issue #186: Update run-tests.sh for easier usage

PR for https://github.com/backdrop/backdrop-issues/issues/186.

This makes working with the run-tests.sh script easier. It implements all the suggestions from the issue as well as allowing a more liberal interpretation of input options. For example options like --color can come after the list of tests, and any option can be specified with an "=" to set the value, or a space like before. Now both of these work: `--url http://localhost` or `--url=http://localhost`. Quotes are also allowed in either approach.