provision/docker: storing the HostPort in the container collection
provision/docker: fix some tests
provision/docker: simplify container.getAddress method

Now we have this data, we don't need to ask it to docker. Collector will
update it when it change.
router/testing: improve implementation

Actually managing routes and backends :-)
router/testing: make the registered router public

It will be easier to test if the router is public :-)
router/testing: unexport FakeRouter
router/testing: rename Instance to FakeRouter

Now that the type is unexported, we can export the variable.