Feature RFC: allow task failures to trigger non-zero exit codes

On the contrary, it should be true that failures result in non-zero
execute codes -- it's logical Unix behavior. Having this a
non-default behavior guarded by the CLI flag is confusing, and
increases the list of options folks have to understand.

If folks want to ignore the code, it's easy to do so.

I would bet most folks are already expecting ansible to return
non-zero in failure cases and are unaware that it only does so in the
case of syntax error with the playbook.

--Michael