core: Add common methods for runtime log4j setup

Adds Log4jUtils class which contains methods for runtime log4j setup
used in engine-config and engine-manage-domains.

Change-Id: Ic00ea0af643e8c978fd67eb8c56e2329d43e776d
Bug-Url: https://bugzilla.redhat.com/1063901
Bug-Url: https://bugzilla.redhat.com/1083411
Signed-off-by: Martin Perina <mperina@redhat.com>