Use pg_ctl for readiness check

Using `pg_ctl status` is more reliable than relying checking an
open port via netcat.

scripts/start-hydra.sh

@@ -1,7 +1,7 @@
 #!/bin/sh
 
-# wait for postgresql to listen
-while ! nc -z localhost 64444; do sleep 1; done
+# wait for postgresql to be up
+while ! pg_ctl -D $(pwd)/.hydra-data/postgres status; do sleep 1; done
 
 createdb -h $(pwd)/.hydra-data/postgres -p 64444 hydra