Add linux support for test suite

I've noticed that the `test` grunt task failed to run on linux completely, hence no spec could be run. I've refactored the tasks a bit to allow running all test cases on a linux machine (tested on Linux Mint 16 x64). 
Another thing is the usage of `--log-file=ci.log` flag that smells to me like CI (haven't looked any deeper) and I thought that it would be a waste to enable it only on windows, so I have changed it to a separate switch to `test` task. I'm not sure it that's the best way to do it (maybe a command line option would be better?) but I wanted to make this change compatible with other behavior so that all scripts that are already using it won't break.