Fix authorization checks for simple_usage.show
Fix authorization checks for simple_usage.show

 * Normal users shouls be allowed to query their own usage info
 * Fixes bug 921327
 * Address bcwaldon's comment about using a default {} in authorize
 * Remove is_admin references
 * Rebase and change expected auth failure response from 401 to 403
 * Remove policy-related tests
 * Add back test_verify_show_cant_view_other_tenant, implemented with test policy

Change-Id: Ib0ce46419b7aedad34de957bfe2e60b10c5af11c

n0ano/ganttclient