Remove hardcoded values

The directory path "/opt/stack/new" is spread across multiple
places in post_test_hook.sh and pre_test_hook.sh files, which
makes it difficult to edit those files in case the destination
directory is different.

Change-Id: Ic74058e6fe5d5876f3a48632b931c1eb8a16e179
Merge "Remove hardcoded values"