mash

Give bodhi2 the ability to mash. Once we can do this in koji, it'll be easy to make local/remote mashing configurable. 
The failed mash stdout/stderr will be logged by this point. This exception is simply to cause the MasherThread to save state & bail out. In the logs there will show 2 exceptions, 1 from mash returning a !0 error code, and then this one to bail out of the other thread.