By switching to block style (`|`) with clip (no `-` or `+`) the failure
messages don't require quoting and gain a single trailing newline. This causes
Ansible to print them as block style, when using the yaml stdout callback
plugin. As a result the values have one less layer of quoting and quote
escaping, making them much easier to read.
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.
Alex Willmer