Add functionality for evergreen.yml to know when resmoke finishes

Once resmoke starts running hang-analysis, the timeout section of evergreen.yml will need to block until the resmoke process has finished, to ensure that analysis (and archival, if specified) has completed.

There are a couple thoughts on how to do this, but the one we've currently settled on is for resmoke to write out to a file when it begins running, and then delete the file right before shutdown.