Convert one further use of 'command -v' into the function command_exists

weaver/weave

@@ -123,7 +123,7 @@ case "$COMMAND" in
     stop)
         docker kill weave > /dev/null
         docker rm weave > /dev/null
-        if command -v conntrack >/dev/null 2>&1
+        if command_exists conntrack
         then
             conntrack -D -p udp --dport 6783 >/dev/null 2>&1
         else