Landscape-server charm should restart Landscape services after license change

This occurred on revision 111 of the landscape-server charm.

We hit https://bugs.launchpad.net/landscape-charm/+bug/2059286, i.e. a peer of mine applied a non-base64-encoded license file to the license_file setting, and the charm still tried to render it, resulting in an /etc/landscape/license.txt file that looks like a binary blob.

When I noticed and corrected the error, landscape-server did not automatically restart correctly. I ended up needing to restart services myself - in my lazy case, opting to simply restart the landscape-server machines - to get them to come up.