remote: provide output listener for command execution

remote: provide output listener for command execution

This listener interface will allow users of the ICommandShell to provide
2 callback methods to get intermediate results for the standard and
error output. Useful for long lasting command executions.

Change-Id: Ibc90bfd679226eee7ef34f170b63abd819bb75e5
Signed-off-by: Bernd Hufmann <Bernd.Hufmann@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/61586
Reviewed-by: Hudson CI
Reviewed-by: Patrick Tasse <patrick.tasse@gmail.com>
Tested-by: Patrick Tasse <patrick.tasse@gmail.com>