extract_utils: Detect output existence before moving it for backup

 * Avoids:
    Cleaning output directory (./../../../vendor/.../.../proprietary)..
    mv: cannot stat './../../../vendor/.../.../proprietary/*':
    No such file or directory

Change-Id: I3258e64f3997f139d8db4fb4e07d14964a469c78
(cherry picked from commit 3c6bdac7)