symbiosis-configure-ips doesn't remove IPs it added once they are removed from /srv/*/config/ip

[patch0]

If an IP has been added to a machine via /srv/*/config/ip, then if removed, it won't be removed from the configuration until next reboot when it won't be re-added.

This is likely as it can't be determined that Symbiosis added the IP, so we should probably either:

1. Make it clear in the docs that removing an IP will need a reboot or manual change via ip.
2. Automatically remove any IPs not set somewhere in /srv/*/config/ip when running symbiosis-configure-ips.
3. Provide a --force switch (like the other Symbiosis apps) to make the config match what symbiosis-configure-ips is trying to do.

Originally reported on Bytemark's Gitlab by @pcammish on 2017-05-02T11:03:24.561Z

[patch0]

This logic would remove IPs that the user has configured in /etc/network/interfaces so we'd need to think carefully here :)

Originally posted by @patch0 on 2017-05-10T20:44:00.248Z

[patch0]

At the moment IPs are added, and no state is kept when things are added/removed. A --force flag could do the trick, but we'd want to be careful not to remove the "main" IP :)