scripts: add clean of build dir to dl_cleanup script

scripts: add clean of build dir to dl_cleanup script

Improve dl_cleanup by adding an option to also clean the build directory
related to the downloaded package.
The script will check every directory in build_dir/ and check if any
old package is present there. If outdated package are found, the old
one are cleared leaving only the last one.

Signed-off-by: Ansuel Smith <[email protected]>