Add suport for availability zones

Neutron supports availability zones but only for DHCP and L3 agents.

Change-Id: I70f7bf35ef94d8e08b6aff9b20adb827278f024e
diff --git a/README.rst b/README.rst
index 9b98a4d..0e61e76 100644
--- a/README.rst
+++ b/README.rst
@@ -278,6 +278,7 @@
         local_ip: 192.168.20.20 # br-mesh ip address
         dvr: False
         agent_mode: legacy
+        availability_zone: az1
         metadata:
           host: 127.0.0.1
           password: pass
@@ -387,6 +388,7 @@
         local_ip: 192.168.20.20 # br-mesh ip address
         dvr: True
         agent_mode: dvr_snat
+        availability_zone: az1
         metadata:
           host: 127.0.0.1
           password: pass
@@ -417,6 +419,7 @@
         dvr: True
         external_access: True     
         agent_mode: dvr
+        availability_zone: az1
         metadata:
           host: 127.0.0.1
           password: pass