Ansible 2.3/Python 2.4 work revealed there is no guarantee a slow target
will have written the initial job status file out before a fast
controller makes an initial check for it. Therefore, provide AsyncRunner
with a sender it should send a message to when the initial job file has
been written.
As a bonus, also catch and report exceptions happening early in
AsyncRunner, rather than leaving them to end up in -vvv output.
And by "compatible" I mean "terrible". This does not implement async job
timeouts, but I'm not going to bother, upstream async implementation is
so buggy and inconsistent it resists even having its behaviour captured
in tests.