Don't check docker version when run --local

The standard case for --local is when the weave script in the weaveexec container
is run by the weave script, which has just checked the version.

--local is also used from weave-kube where we don't mount the docker socket and
therefore cannot check.

Since --local is undocumented we will not worry about any other cases; the worst
that can happen is a confusing error message.

weave

@@ -219,8 +219,6 @@ kill_container() {
 # main
 ######################################################################
 
-check_docker_version
-
 [ "$1" = "--local" ] && shift 1 && IS_LOCAL=1
 
 # "--help|help" are special because we always want to process them
@@ -245,6 +243,7 @@ elif [ "$1" = "env" -a "$2" = "--restore" ] ; then
 fi
 
 if [ -z "$IS_LOCAL" ] ; then
+    check_docker_version
     exec_remote "$@"
     exit $?
 fi