Handle highway=mini_roundabout the same way as junction=roundabout during routing

Currently the osm node highway=mini_roundabout is being handled as a normal junction instead of a roundabout during routing with osm maps in Germany. But this is confusing since the instruction given, e.g. "turn
left", is somewhat wrong and should be e.g. "enter the roundabout and
take the 2nd exit".

Note that a "mini_roundabout" is not necessary small; in fact it can be quite large. See the osm wiki page for more details.