Added policy for lbaas v2 agent extension resource

Adding get_agent-loadbalancers policy only because v2 can
reuse the get_loadbalancer-agent policy from v1.
get_loadbalancer-pools doesn't make sense as a policy for
v2 because pools are no longer the root object.

Change-Id: Ic9179ef0a95b91d1b7662537fffeb0a949efc925

etc/policy.json

@@ -114,6 +114,7 @@
     "get_l3-agents": "rule:admin_only",
     "get_loadbalancer-agent": "rule:admin_only",
     "get_loadbalancer-pools": "rule:admin_only",
+    "get_agent-loadbalancers": "rule:admin_only",
 
     "create_floatingip": "rule:regular_user",
     "create_floatingip:floating_ip_address": "rule:admin_only",