cannot run weave inside a container that has PROCFS set

If the script is ran from a container that had already been started with -v /proc:/hostproc -e PROCFS=/hostproc and --local is not passed in, it will pickup the value of $PROCFS and try to start weaveworks/weaveexec with -v /hostproc:/hostproc, for which Docker will bind an empty directory as /hostproc doesn't exist on the host itself.