Add tests for wallaby's behavior when starting chromedriver

[aaronrenner]

This adds some initial test coverage around how wallaby starts the chromedriver executable. I figured I should add some test coverage to protect the existing behavior before making changes to address #509.

Since chromedriver is started on wallaby's application startup, these tests

1. stop wallaby
2. make the necessary environment changes (to use fake script and chromedriver as main driver)
3. starts wallaby

The benefit of the FakeChromedriverScript is we can record the arguments that chromedriver is being started and assert that default and user configured options are passed correctly. It also makes it much simpler to test checks like running against an old version of chromedriver.

[aaronrenner]

I'm realizing I have a little more work to do on these test helpers that generate the fake chromedriver script. I'm going to close this PR and open a new one when I'm done changing things.