oslo-config: 4.11.0 -> 4.12.0, fix build

also updated the following dependencies:
keystoneauth1: 3.1.0 -> 3.2.0
  disabled tests which require oslo-config, oslo-test or requests-kerberos
oslo-i18n: 2.7.0 -> 3.18.0
oslotest: 1.12.0 -> 2.18.0
os-client-config: 1.8.1 -> 1.28.0
  needed to disable testing due to circular dependency with oslotest
mox3: 0.11.0 -> 0.23.0
  disable tests for py36 due to upstream bug
debtcollector: 0.9.0 -> 1.17.0
  tests enabled

extra packages:
requestsexceptions: init at 1.3.0