After removing keystone API v2, trove requires that
trove_auth_url parameter has the v3 URL. Note that
versionless url is not valid for trove_auth_url so
this patch enforces v3 url even when auth_url is
not versioned.
Additionally, the default value for auth_url parameter
has been updated to point to v3.
Change-Id: I8d0e200958c813101d72e180c6da8343b5fcae6e