Jenkins plugin with color according to test score

Coming back to you with a pull request.  I tried to formalize this enhancement, though I'm not very familiar with Ruby, so bear with me.

Method watch_test_server can be applied on light with 3 parameters (Jenkins server URL, Net::HTTP::Proxy which can be nil, and job name)

Color depends on last job result.
Job failed or tests failed = red light
Job successful and all tests pass = blue light
From 1% to 99% test result, gradient from orange to greenish-blue.

If you think this could be generalized, don't hesitate.  Waiting for your comments on this.

Regards,

thebignet