cleanup-workdir: add a script to clean up WORKDIR

cleanup-workdir: add a script to clean up WORKDIR

[Yocto 1561]
Add script cleanup-workdir to clean up WORKDIR. It checks every
package build directories under WORKDIR then parse the directory
name to get package name and version. If the version is not the
package prefer version then delete the directory.

Signed-off-by: Kang Kai <kai.kang@windriver.com>