Rework how config vars are sourced

- ensure we source config/functions from the correct directory
- move config sourcing up before DOKKU_TRACE to reduce trace output

functions

@@ -1,6 +1,6 @@
 #!/usr/bin/env bash
+source "$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)/config"
 set -eo pipefail; [[ $DOKKU_TRACE ]] && set -x
-source "$(dirname "$0")/config"
 source "$PLUGIN_AVAILABLE_PATH/config/functions"
 
 get_random_ports() {