collect coverage data with onSpecComplete method

To support the end2end test covergare scenario it was needed to collect the coverage
result with onSpecComplete instead of onBrowserComplete. This new behavoir is configurable and has to be activated with the following karma configuration parameter thresholdEnd2EndTests.

I know this is not a good name for the configuration parameter, naming is not my strength. Very good tool i used for some of my projects to fail a build on travis if the coverage rules are not fulfilled.