Add fake sudo script

Manila tests use sudo all over the place and while the only
configured user in the test image is root, it's easier to
fake the sudo binary than to modify test code to know when
to sudo and when to not.

Also remove 2 mkdir calls that are obviated by the new file
getting copied in those directories.

Change-Id: Ib0cbe05130bc617154bf471e2ecc0a78b2bb8377

common-files/usr/bin/sudo

@@ -0,0 +1,4 @@
+#!/bin/sh
+
+$@
+

run-buildroot.sh

@@ -23,14 +23,12 @@ fi
 if [ ! -d overlay-client ] ; then
     mkdir overlay-client
     cp -a common-files/* overlay-client
-    mkdir -p overlay-client/usr/bin
     cp $JSON_SH overlay-client/usr/bin
 fi
 if [ ! -d overlay-server ] ; then
     mkdir overlay-server
     cp -a common-files/* overlay-server
     cp -a server-files/* overlay-server
-    mkdir -p overlay-server/usr/bin
     cp $JSON_SH overlay-server/usr/bin
 fi