updated content_type in the exception where it is missing.
updated content_type in the exception where it is missing.

Fixes bug 1184279

Added missing content_type in HTTPConflict, while attempting to upload a duplicate image.

Change-Id: I4dbef69b6f9e83d4b5090cc0bbfcb01611c05a37

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