Otherwise there can be duplicate beans with the same type and different
names, becasue the autoconfig does not (for some reason) use
@EnableConfigurationProperties to create the ServerProperties bean.

It isn't an issue until someone writes some autoconfig that itself
imports the ZuulConfiguration (i.e. regular concious users of
@EnableZuulServer do not see any problems and hence no tests fail
here or in integration projects).

Fixes gh-821