Kea might not use getopt correctly on alpine

On all the alpine systems in jenkins, we have this failure:

netconf_controller_unittests.cc:134
Expected equality of these values:
  std::string(ex.what())
    Which is: "unsupported option: [x] d2-test-config.json"
  "unsupported option: [x] "

It's not related only to NETCONF. The tests there are just more thorough and check for the error message and that's why it appears only there. The tested code is common to all binaries.

The tested argument is just -x. It could be that on alpine systems, the way Kea uses getopt in DControllerBase::parseArgs() doesn't clear an argument previously used in the same unit test, which would be why d2-test-config.json appears in the error message.

You can see the failures here: https://jenkins.aws.isc.org/job/kea-dev/job/ut-extended/1017/.