Nosetests fail when run with processes

When run with the version on master and a setup.cfg with

    processes=8
    process-timeout=120

I get:

    	AttributeError: 'NoneType' object has no attribute 'exclude'

The line in question is:

    self.coverInstance.exclude('#pragma[: ]+[nN][oO] [cC][oO][vV][eE][rR]')

So `self.coverInstance` is `None`. Making this check for `self.coverInstance` allows the tests to run.

This is a temporary fix, I imagine, It looks like there are several bugs already posted against multiprocessing.