allow configurable test names per url

[emmettbutler]

I run Saucelabs builds containing multiple versions of my test suite, each as a different Saucelabs "test" instance:

This list comprises two different versions of the suite specified by two different values for the grunt-saucelabs url option, each being run on six different browser/OS combinations.

I'd like to be able to see at a glance on this screen which url a given test is using. A way to do this via grunt-saucelabs could be to change this logic to select the testname by looking up the test's url in a mapping. This mapping might be passed through the options object in the Gruntfile, and would map url values to testname values.