Fix brctl calls

Some distros no longer ship brctl, iproute2 should be used
in its place. The linuxbridge agent plugin script was still
using it, as was worlddump, which generates this warning on
a failure:

    Running devstack worlddump.py
    /bin/sh: 1: brctl: not found

Conditionalizing worlddump based on whether brctl is installed
to make this go away.

Change-Id: Iafbf4038bab08c261d45d117b12d4629ba32d65e

Author: Brian Haley

lib/neutron_plugins/linuxbridge_agent

@@ -48,7 +48,7 @@ function neutron_plugin_configure_dhcp_agent {
 
 function neutron_plugin_configure_l3_agent {
     local conf_file=$1
-    sudo brctl addbr $PUBLIC_BRIDGE
+    sudo ip link add $PUBLIC_BRIDGE type bridge
     set_mtu $PUBLIC_BRIDGE $PUBLIC_BRIDGE_MTU
 }
 

tools/worlddump.py

@@ -165,7 +165,8 @@ def network_dump():
     _header("Network Dump")
 
     _dump_cmd("bridge link")
-    _dump_cmd("brctl show")
+    if _find_cmd("brctl"):
+        _dump_cmd("brctl show")
     _dump_cmd("ip link show type bridge")
     ip_cmds = ["neigh", "addr", "link", "route"]
     for cmd in ip_cmds + ['netns']: