Suppressing of autorunning of specs

I'm using `grunt-jasmine-istanbul` to generate a specfile with instrumented src files so that when grunt runs my tests it also generates a coverage report. 

But I also want a specfile which contains the original src files, and this specfile should never be run in phantomjs as it's intended purely for debugging in the browser.

My approach is to define two grunt-contrib-jasmine subtasks, one of which uses the istanbul template, and the other the default. The default one I would like to suppress from running in grunt, hence the addition of this `run` option