Give -iprange a default, and check if it is free

weave

@@ -984,6 +984,14 @@ case "$COMMAND" in
             esac
         done
         eval "set -- $ARGS"
+        if [ -z "$IPRANGE" ] ; then
+            IPRANGE="-iprange 10.128.0.0/9"
+            if ! netcheck ${IPRANGE#* } ; then
+                echo "Default" $IPRANGE "overlaps with existing route." >&2
+                echo "Please pick another range and set it on all hosts." >&2
+                exit 1
+            fi
+        fi
         # Set WEAVE_DOCKER_ARGS in the environment in order to supply
         # additional parameters, such as resource limits, to docker
         # when launching the weave container.