* Fix exec parameter parsing (#580)
Exec seems to be broken by ad6fbba806
This change basically copies what's in remotecommand.NewOptions, just
without the logging.
(cherry picked from commit 449eb3bb7d)
* Don't set cancel function to nil on error
Backported from ceb9b16c5c
* Define and use an interface for logging.
This allows alternative implementations to use whatever logging package
they want.
Currently the interface just mimicks what logrus already implements,
with minor modifications to not rely on logrus itself. I think the
interface is pretty solid in terms of logging implementations being able
to do what they need to.
* Make tracing interface to coalesce logging/tracing
Allows us to share data between the tracer and the logger so we can
simplify log/trace handling wher we generally want data to go both
places.
