Duplicate gitaly init variables in 'default' file

This is needed because these variables depend (directly or indirectly)
on the 'app_root' variable which can be changed in the default file.
If app_root has a non-standard value, the value of e.g. gitaly_dir
generated in the init script becomes invalid.

Author: jacobvosmaer

lib/support/init.d/gitlab.default.example

@@ -87,4 +87,6 @@ shell_path="/bin/bash"
 
 # This variable controls whether the init script starts/stops Gitaly
 gitaly_enabled=false
+gitaly_dir=$(cd $app_root/../gitaly 2> /dev/null && pwd)
+gitaly_pid_path="$pid_path/gitaly.pid"
 gitaly_log="$app_root/log/gitaly.log"