The check that the two MaxScales have the same services is now in a common
function. Added more details into the error message as to why the command
failed. The hosts and their extra services are logged for both the source
and target of the command.
The `cluster diff` command could display the extra services in the diff
but this could be interpreted as a sign that MaxScale could act on that
part of the diff. Returning an error instead of silently ignoring the
extra services should allow for a more consistent user experience.
70ae93a9ab