improve docker build and wait for memcached

entry.sh

@@ -0,0 +1,11 @@
+#!/bin/ash
+
+echo "Waiting for memcached"
+
+while ! nc -z -w 1 memcached 11211; do   
+  sleep 1
+  echo "..."
+done
+
+echo "Starting server"
+/app/cryptgeon