Add better user feedback when bind is not implemented
Add better user feedback when bind is not implemented

Rather than raise a 501 with a generic message, this will provide users
with specific feedback about what exactly in their authentication
request triggered the 501.

Change-Id: I85a22dd6ba4b6ea9b7d29f532c2fb5adee9576e9

ajayaa/keystone,takeshineshiro/keystone,roopali8/keystone,jamielennox/keystone,dstanek/keystone,dstanek/keystone,ilay09/keystone,mahak/keystone,rajalokan/keystone,klmitch/keystone,himanshu-setia/keystone,openstack/keystone,dstanek/keystone,rajalokan/keystone,cernops/keystone,dims/keystone,dims/keystone,roopali8/keystone,takeshineshiro/keystone,maestro-hybrid-cloud/keystone,ajayaa/keystone,cernops/keystone,jonnary/keystone,ilay09/keystone,openstack/keystone,ilay09/keystone,vivekdhayaal/keystone,maestro-hybrid-cloud/keystone,openstack/keystone,idjaw/keystone,klmitch/keystone,idjaw/keystone,mahak/keystone,jonnary/keystone,rajalokan/keystone,mahak/keystone,vivekdhayaal/keystone,jamielennox/keystone,himanshu-setia/keystone,vivekdhayaal/keystone