Fixes for issue #194

We now use ip address instead of hostname for generating test urls.

You can now also manually override the hostname used, either on the command-line with the new `--hostname foo.com` flag, or through the config file with the `hostname` top level property.
Merge remote branch 'origin/issue_194' into issue_194

* origin/issue_194:
  Fixes for issue #194

Conflicts:
	lib/constants.js
	lib/executor.js
	test/specs/constants.spec.js