log: Workaround missing getChild in python 2.6

Logger.getChild() is missing in python 2.6, so we need to work around
this.
Done by emulating getChild.

Change-Id: Ie22fb60025a8de54d9044281fe964c081bb6ebaf
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1013461
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>