Horizon will by default check that a project has
a router with a port on an external network prior
to allowing floating ips to be attached to
instances. Since it is valid to use a shared
router from a different project we make this
configurable to allow disabling this check.
Closes-Bug: #1815032
Change-Id: I5c3e44e5daa683e14ac39979d6e9a7c2238dd120