Improve status reporting in the UI plugin

This patch improves:
- solution status reporting
- error reporting when start or migrate action fails
- error reporting when cancel optimize start call fails
- button behaviour when pressed and action was successful
- synchronization of buttons with VM state

Change-Id: I629abdbd5bf2bf299cbdbeca95cc905af7089ac1
Signed-off-by: Martin Sivak <msivak@redhat.com>