Using LOG.warning replace LOG.warn
Using LOG.warning replace LOG.warn

This patch replaces LOG.warn by LOG.warning on
https://github.com/openstack/horizon/blob/master/openstack_dashboard/api/keystone.py#L222
to avoid DeprecationWarning.

Change-Id: I8cd9ea6778b356c3b1f4e0c6e95feb096792c58d
Closes-Bug: #1562731

wolverineav/horizon,bac/horizon,wolverineav/horizon,NeCTAR-RC/horizon,wolverineav/horizon,openstack/horizon,openstack/horizon,sandvine/horizon,bac/horizon,bac/horizon,coreycb/horizon,BiznetGIO/horizon,BiznetGIO/horizon,ChameleonCloud/horizon,NeCTAR-RC/horizon,yeming233/horizon,NeCTAR-RC/horizon,noironetworks/horizon,noironetworks/horizon,NeCTAR-RC/horizon,noironetworks/horizon,Mirantis/mos-horizon,coreycb/horizon,yeming233/horizon,BiznetGIO/horizon,ChameleonCloud/horizon,Mirantis/mos-horizon,openstack/horizon,Mirantis/mos-horizon,sandvine/horizon,openstack/horizon,bac/horizon,Mirantis/mos-horizon,noironetworks/horizon,bigswitch/horizon,bigswitch/horizon,ChameleonCloud/horizon,bigswitch/horizon,coreycb/horizon,sandvine/horizon,bigswitch/horizon,BiznetGIO/horizon,ChameleonCloud/horizon,yeming233/horizon,yeming233/horizon,coreycb/horizon,wolverineav/horizon,sandvine/horizon