Combine the ExitStatus and Err values from remote.Cmd into an error
returned by Wait, better matching the behavior of the os/exec package.
Non-zero exit codes are returned from Wait as a remote.ExitError.
Communicator related errors are returned directly.
Clean up all the error handling in the provisioners using a
communicator. Also remove the extra copyOutput synchronization that was
copied from package to package.
The remote.Cmd struct could not convey any transport related error to
the caller, meaning that interrupted commands would show that they
succeeded.
Change Cmd.SetExited to accept an exit status, as well as an error to
store for the caller. Make the status and error fields internal,
require serialized access through the getter methods.
Users of remote.Cmd should not check both Cmd.Err() and Cmd.ExitStatus()
until after Wait returns.
Require communicators to call Cmd.Init before executing the command.
This will indicate incorrect usage of the remote.Cmd by causing a panic
in SetExitStatus.
This is needed as preperation for adding WinRM support. There is still
one error in the tests which needs another look, but other than that it
seems like were now ready to start working on the WinRM part…
