Only add logging handlers if there currently aren't any
Only add logging handlers if there currently aren't any

This corrects an odd problem where Horizon would stand up multiple
client objects, which would cause duplicate/triplicate/dozens of
repeated log lines in its log files, due to multiple identical
handlers being added to the logging object

Fixes Bug 1182678

Change-Id: I020b3999c9008b996286ccb74a7801c96c43e71c

metacloud/python-keystoneclient,klmitch/python-keystoneclient,Mercador/python-keystoneclient,citrix-openstack-build/python-keystoneclient,darren-wang/ksc,citrix-openstack-build/python-keystoneclient,ntt-sic/python-keystoneclient,jamielennox/python-keystoneclient,ging/python-keystoneclient,ntt-sic/python-keystoneclient,magic0704/python-keystoneclient,ging/python-keystoneclient,sdpp/python-keystoneclient,magic0704/python-keystoneclient,sdpp/python-keystoneclient,metacloud/python-keystoneclient,klmitch/python-keystoneclient,darren-wang/ksc,alexpilotti/python-keystoneclient,Mercador/python-keystoneclient,citrix-openstack-build/python-keystoneclient,jamielennox/python-keystoneclient,alexpilotti/python-keystoneclient,jamielennox/python-keystoneclient,ntt-sic/python-keystoneclient