DEV: Use docker links to set password environment variable in the hub.

Also, yell at people if they use the default password.

examples/postgres/db/initdb.sh

@@ -1,5 +1,16 @@
 #!/bin/bash
 
+echo "";
+echo "Running initdb.sh.";
+if [ -z "$JPY_PSQL_PASSWORD" ]; then
+    echo "Need to set JPY_PSQL_PASSWORD in Dockerfile via command line";
+    exit 1;
+elif [ "$JPY_PSQL_PASSWORD" == "arglebargle" ]; then
+    echo "WARNING: Running with password!"
+    echo "You are STRONGLY ADVISED to use your own password.";
+fi
+echo "";
+
 # Start a postgres daemon, ignoring log output.
 gosu postgres pg_ctl start -w -l /dev/null