Revert "use which to detect if python2 exists, oneric does not have python2"

This reverts commit 7eb05edcd8ab3bfd4c938c1eb5028cfce584270b.
Revert "Trimmed the branch to only the openrtm_aist_python sub directory"

This reverts commit ac2987cba122d2b7301347e21c1bbbac5cf8ed5b.
Rebase from 'upstream' (no changes)
Trimmed the branch to only the openrtm_aist_python sub directory
use which to detect if python2 exists, oneric does not have python2