A script to clean obsolete sstate cache files

A script to clean obsolete sstate cache files

There would be many obsolete cache files in the SSTATE_DIR after several
builds, this script can remove the obsolete one for a pkg, only leave
the up to date one.

Here is the help text:

sstate-cache-management.sh <OPTION>

Options:
  --help, -h
        Display this help and exit.

  --cache-dir=<sstate cache dir>
        Specify sstate cache directory, will use the environment
        variable SSTATE_CACHE_DIR if it is not specified.

  --remove-duplicated
        Remove the duplicated sstate cache files of one package, only
        the newest one would be kept.

[YOCTO #1682]

(From OE-Core rev: 7c99ef6d2173b14e1109a540ee5ae47b56d707e7)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>