Change SpecRunner to run more than one suite, fix issues in tests

After this change, instead of running "all", the Jenkins machines will run ``grunt test-integration --suite="unit,extension"`` only.

I made some attempts to fix issues in the integration suite, but I wasn't able to fix all issues, particularly intermittent NodeConnection and LiveDevelopment issues that seem to only reproduce on the build machines.

A short summary:
* fixes NativeFileSystem where calling ``readEntries`` on an empty path would read the entire disk
* fixes LiveDevelopment launcherUrl when run from SpecRunner.html
* Sync up SpecRunnerUtils mock document implementation with the latest from DocumentManager

There also appears to be a memory leak when running unit tests that I did not have time to pin down. I'd like to get at least these changes in ASAP in order to get Jenkins running again.