BZ #1085547 - Keystone role is created as _member_ instead of Member

https://bugzilla.redhat.com/show_bug.cgi?id=1085547

Keystone itself creates as the default '_member_', and horizon incorrectly
assumes a default of 'Member'.  However, the horizon config does take a param
called 'keystone_default_role', so we now set that to match the keystone default.