Stop running services if the user wants to change provider.

**DO NOT MERGE**

If the user changes the selected provider, we ask if he wants to stop the running servers since is needed to do the change.

Right now there is a problem that when the services are stopped, the EIP widget seems to have the firewall up (has two buttons)... working on it.
assert what?
`self._selected_provider_index` is initialized with `-1`, so in the worst case gets into an state where nothing is selected.
Since we load the providers and launch the wizard if we don't have any, I'm almost sure that that case won't happen.