Job name escaping and an addition to the Jenkins root URL.

Hi,

Thanks for your work on this gem.

I have changed a couple of things so that they work in my set up.

1. Our Jenkins server has an Apache HTTP server in front of it so the root URL is something like http://ci-server/jenkins. I have added jenkins_path to cope with this.
2. Some of our Jenkins jobs have spaces in the name so I have added a method to escape them before they are added to the REST call.

All the unit test pass with these changes. The functional tests do not but they did not in the version I forked.

Regards,

Kevin