Continuation of: #11660, working on issue #11626.
Wrapped portmapper global state into a struct. Now portallocator and
portmapper have no global state (except configuration, and a default
instance).
Unfortunately, removing the global default instances will break
```api/server/server.go:1539```, and ```daemon/daemon.go:832```, which
both call the global portallocator directly. Fixing that would be a much
bigger change, so for now, have postponed that.
Signed-off-by: Paul Bellamy <paul.a.bellamy@gmail.com>
87df5ab41b