Allow keystoneclient to work with older keystone installs
Allow keystoneclient to work with older keystone installs

Older keystone installs may return 501 for GET / instead of 300
like today. We should be able to assume that if 501 is returned the
server will support v2.0 only.

Fixes bug 1159911

Change-Id: If264840d8678a490264f1bdb62f1b51c362619e1

citrix-openstack-build/python-keystoneclient,klmitch/python-keystoneclient,alexpilotti/python-keystoneclient,sdpp/python-keystoneclient,magic0704/python-keystoneclient,Mercador/python-keystoneclient,alexpilotti/python-keystoneclient,jamielennox/python-keystoneclient,ntt-sic/python-keystoneclient,jamielennox/python-keystoneclient,citrix-openstack-build/python-keystoneclient,Mercador/python-keystoneclient,magic0704/python-keystoneclient,metacloud/python-keystoneclient,ging/python-keystoneclient,ntt-sic/python-keystoneclient,klmitch/python-keystoneclient,citrix-openstack-build/python-keystoneclient,darren-wang/ksc,metacloud/python-keystoneclient,ntt-sic/python-keystoneclient,darren-wang/ksc,ging/python-keystoneclient,sdpp/python-keystoneclient,jamielennox/python-keystoneclient