proxy needs to add weavewait to execs as well

Bug came up in a test where we are restarting and doing an exec checking
a network interface right away. weavewait is only added if the container
has a WEAVE_CIDR var set, the same as at container creation.

test/config.sh

@@ -97,6 +97,14 @@ exec_on() {
     docker -H tcp://$host:2375 exec $container "$@"
 }
 
+proxy_exec_on() {
+    host=$1
+    container=$2
+    shift 2
+    docker -H tcp://$host:12375 exec $container "$@"
+}
+
+
 start_container() {
     host=$1
     shift 1