Control concurrency of on-local-blogs via environment variable

bin/on-all-blogs

-#!/bin/bash
+#!/bin/sh
 #
 # Run a 'noblogs' command on all blogs.
 #

bin/on-local-blogs

-#!/bin/bash
+#!/bin/sh
 #
 # Run a 'noblogs' command on just those blogs that are hosted
 # on this server.
@@ -16,5 +16,4 @@ dir=${dir:-.}
 abs_dir=$(cd ${dir} && pwd)
 
 ${dir}/noblogs print-local-blogs | grep -v Warning \
-    | xargs -n 30 ${abs_dir}/noblogs "$@"
-
+    | xargs -n ${CONCURRENCY:-30} ${abs_dir}/noblogs "$@"