Don't WARN if trying to add a scheme which exists.
Don't WARN if trying to add a scheme which exists.

Updates the register_scheme_map function in store/location.py so that
it registers new scheme maps only if they don't already exist.
Also, removes the warning message that was previously logged if
a duplicate entry was found. Since both Glance v1 and v2 controllers
attempt to register scheme's this seems reasonable and shouldn't cause
any problems with how things work.

This fixes an issue where Glance API logs always had warning messages
stating it was 'Overwriting scheme' information even though everything
is configured correctly.

Fixes LP Bug #1050711.

Change-Id: Ief539187f9c64a3b2de6d431b1e2ffc9e07e5c90

ntt-sic/glance,JioCloud/glance,paramite/glance,tanglei528/glance,darren-wang/gl,stevelle/glance,jumpstarter-io/glance,rajalokan/glance,takeshineshiro/glance,stevelle/glance,ntt-sic/glance,ozamiatin/glance,openstack/glance,cloudbau/glance,rajalokan/glance,scripnichenko/glance,tanglei528/glance,rickerc/glance_audit,darren-wang/gl,sigmavirus24/glance,redhat-openstack/glance,wkoathp/glance,paramite/glance,openstack/glance,citrix-openstack-build/glance,SUSE-Cloud/glance,klmitch/glance,dims/glance,saeki-masaki/glance,scripnichenko/glance,vuntz/glance,saeki-masaki/glance,SUSE-Cloud/glance,wkoathp/glance,kfwang/Glance-OVA-OVF,klmitch/glance,akash1808/glance,akash1808/glance,rickerc/glance_audit,vuntz/glance,sigmavirus24/glance,citrix-openstack-build/glance,redhat-openstack/glance,takeshineshiro/glance,JioCloud/glance,ozamiatin/glance,cloudbau/glance,kfwang/Glance-OVA-OVF,dims/glance,jumpstarter-io/glance,openstack/glance