lib/oe/reproducible.py: Fix git HEAD check
The check for a git HEAD still wasn't quite correct because it was using
the .git directory as the current working directory. Instead, it should
be passed as the --git-dir argument when running git. Running `git
rev-parse HEAD` in a .git directory with no HEAD reports 'HEAD' and
exits with success but then 'git log' will fail, which is not what we
want.
Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit
cdbd47dd7e1657b91b65a0940b7cbf119764240f)
Signed-off-by: Steve Sakoman <steve@sakoman.com>
