This module adds the ability to Log4j Core to use Kubernetes attributes
in a configuration file.

It is a cleaned-up version of the
`org.apache.logging.log4j:log4j-kubernetes`.

As explained in fabric8io#5682, it does make more sense to host is here since:

 * it only depends on a very stable `StrLookup` dependency from
   `log4j-core`,
 * the number and kind of properties available through
   `kubernetes-client` depend on its version.

Adds a `kubernetes.log4j.useProperties` Java system property to disable
the usage of Log4j properties.

Increases test coverage.