As of now promoting (or demoting) a node that has its role
left unchanged will always print a successful message.
This PR fixes the issue by matching the behavior on swarmkit's
swarmctl command and printing a message when desired role is
the current role of the node.
As a result this also avoids calling update when it is not
necessary.
Signed-off-by: Alexandre Beslic <alexandre.beslic@gmail.com>
Upstream-commit: 5479df79c7859d5a09f42c22ddb5fa3e56ceeb7c
Component: engine