Override __outputter__ when functions trigger exceptions

For module functions which have an outputter defined in an ``__outputter__``
dict, the specified outputter is used when the function returns data to
the master. However, when an exception generates an error message, such
as when an exception is triggered, the nested outputter is desired.

This commit adds the ability to set an ``out`` key in the dict of return
data passed to ``salt.minion.Minion._return_pub()`` which, if present,
overrides the outputter defined in the ``__outputter__`` dict for that
function.