Skips enabling kernel bridge firewall in container

Calling enable_kernel_bridge_firewall inside a
container, devstack will crash because it tries to
load a kernel module by calling 'sudo modprobe' on
net.bridge.

Change-Id: Id4718c065d5a8c507d49f38e19c2796a64221aa4
Closes-Bug: #1662194

functions

@@ -664,6 +664,16 @@ function set_mtu {
 }
 
 
+# running_in_container - Returns true otherwise false
+function running_in_container {
+    if grep -q lxc /proc/1/cgroup; then
+        return 0
+    fi
+
+    return 1
+}
+
+
 # enable_kernel_bridge_firewall - Enable kernel support for bridge firewalling
 function enable_kernel_bridge_firewall {
     # Load bridge module. This module provides access to firewall for bridged