Annotate 5xx client calls with an error tag

[pavolloffay]

We could add error tag to client spans for returned 5xx codes.

Related issue for async server API #91

[pavolloffay]

The MP-OT spec defines that error tag SHOULD be added only for 4xx (client codes). If the server side is not traced and 5xx is returned I would also consider that operation as failed or errored.

[pavolloffay]

Reported in MP-OT microprofile/microprofile-opentracing#114