In one of the test we want a failure due to a 500 error returned by a
not existing local registry, the fake server address is set to localhost:5000
In a typical local env is quite likely to have a local registry running
and the default address usually is localhost:5000 and that will make the
test to return a 4xx error and not the expected 500 error, this change
just set a not standard port for the fake local registry to reduce the
chances to clash with an existing running one.