Move definition of $PROCFS (cosmetic)

It's not required to be set at the top, it's only looked at down below.

weave

@@ -14,7 +14,6 @@ IMAGE_VERSION=${VERSION:-$IMAGE_VERSION}
 DOCKERHUB_USER=weaveworks
 BASE_EXEC_IMAGE=$DOCKERHUB_USER/weaveexec
 EXEC_IMAGE=$BASE_EXEC_IMAGE:$IMAGE_VERSION
-PROCFS=${PROCFS:-/proc}
 
 usage() {
     echo "Usage:"
@@ -124,6 +123,7 @@ BASE_DNS_IMAGE=$DOCKERHUB_USER/weavedns
 IMAGE=$BASE_IMAGE:$IMAGE_VERSION
 DNS_IMAGE=$BASE_DNS_IMAGE:$IMAGE_VERSION
 
+PROCFS=${PROCFS:-/proc}
 DOCKER_BRIDGE=${DOCKER_BRIDGE:-docker0}
 CONTAINER_NAME=${WEAVE_CONTAINER_NAME:-weave}
 DNS_CONTAINER_NAME=weavedns