Reset runs by client considered in progress when getting next run

Now that the client page does not refresh, a new session (client) isn't created after a test completes. This means that a client is considered "alive" and the cleanup action does not clear it's runs. 

So, on a test which does not heartbeat in time the status never changes from "in progress".

A "getrun" action now clears any old in progress runs for that client based on the following assumption:
 - A client can't be running any other runs if it is requesting a new run.