Set linux:network:bridge = openvswitch for OVS-based interfaces

Automatically set bridge type depending on interface role.

Doesn't support 'linux' bridge type at the moments, because
the salt-formula-linux don't support multiple bridge types
at the moment.

Change-Id: Icbf4a8235bb5e188831a158655f52473a440b929
diff --git "a/\173\173 cookiecutter._env_name \175\175/linux_network_interface.yml" "b/\173\173 cookiecutter._env_name \175\175/linux_network_interface.yml"
index 8474d17..7aa8dd6 100644
--- "a/\173\173 cookiecutter._env_name \175\175/linux_network_interface.yml"
+++ "b/\173\173 cookiecutter._env_name \175\175/linux_network_interface.yml"
@@ -1,6 +1,8 @@
 parameters:
-  # _param:
-  # Put overrides for any environment-specific variables here
+  _param:
+    # Put overrides for any environment-specific variables here
+    linux_network_bridge: 'none'
   linux:
     network:
+      bridge: ${_param:linux_network_bridge}
       interface: ${_param:linux_network_interfaces}