Add allow_global_implied_dsr_disabled feature flag

This patch enabled the "allow_global_implied_dsr_disabled" feature
flag. This is a feature flag toggle for bug 1590578 which is fixed
in Newton and Ocata. This option can be removed after Mitaka is
end of life.

Change-Id: I70e3ce79ee6d9b00cc48bb178bd423d0196f6588
Related-Bug: #1590578
diff --git a/lib/tempest b/lib/tempest
index 128e972..d95a9f5 100644
--- a/lib/tempest
+++ b/lib/tempest
@@ -290,6 +290,10 @@
         iniset $TEMPEST_CONFIG identity-feature-enabled security_compliance True
     fi
 
+    # TODO(rodrigods): This is a feature flag for bug 1590578 which is fixed in
+    # Newton and Ocata. This option can be removed after Mitaka is end of life.
+    iniset $TEMPEST_CONFIG identity-feature-enabled forbid_global_implied_dsr True
+
     # Image
     # We want to be able to override this variable in the gate to avoid
     # doing an external HTTP fetch for this test.