Declare index on ImageMember model
Declare index on ImageMember model

This index was added in migration 008. However, it was not on the model,
which meant any autocreated db would not have it.

Fixes bug 1154777

Change-Id: I34590ffebaf547be9a12e5a85216cda145d9e8db

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