fix test reference files to match comments

Closes #2651 (closed). Should fix CtrlAgentGetCfgTest.simple and NetconfGetCfgTest.simple.

get_config_unittest.cc:290
Value of: isEquivalent(unparsed, jsonj)
  Actual: false
Expected: true

https://jenkins.aws.isc.org/job/kea-dev/job/ut-extended/921/#showFailuresLink