Ensure that debug agent has root_helper in [AGENT] section

This is a temporary fix until the Quantum patch lands. Then
devstack will be updated to remove all of the root_helper
settings in the DEFAULT section.
The Quantum patch in Question is:
https://review.openstack.org/#/c/20603/

Change-Id: Ie17ae76e8b525481e1002bd941812390cf2e2afc
diff --git a/lib/quantum b/lib/quantum
index c5fc6e8..d5733b3 100644
--- a/lib/quantum
+++ b/lib/quantum
@@ -410,6 +410,9 @@
     iniset $QUANTUM_TEST_CONFIG_FILE DEFAULT debug False
     iniset $QUANTUM_TEST_CONFIG_FILE DEFAULT use_namespaces $Q_USE_NAMESPACE
     iniset $QUANTUM_TEST_CONFIG_FILE DEFAULT root_helper "$Q_RR_COMMAND"
+    # Intermediate fix until Quantum patch lands and then line above will
+    # be cleaned.
+    iniset $QUANTUM_TEST_CONFIG_FILE AGENT root_helper "$Q_RR_COMMAND"
 
     _quantum_setup_keystone $QUANTUM_TEST_CONFIG_FILE DEFAULT set_auth_url
     _quantum_setup_interface_driver $QUANTUM_TEST_CONFIG_FILE