classes/populate_sdk_ext: prepend to PATH rather than appending
The rest of the environment setup script prepends to PATH, so when we
add the path to run devtool we should be prepending as well. This
also ensures that when you run the environment setup script from
extensible SDK installation A and then in the same shell session run the
environment setup script from installation B, and then run devtool, that
you're running B's devtool and not A's.
Fixes [YOCTO #9046].
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Ross Burton <ross.burton@intel.com>
