torture: Include commit discription in testid.txt

torture: Include commit discription in testid.txt

Currently, the testid.txt file in the top-level directory of the
rcutorture results contains the output of "git rev-parse HEAD", which
just gives the full SHA-1 of the current commit.  This is followed by
the output of "git status", which is further followed by the output of
"git diff".  This works, but is less than helpful to human readers
scanning a list of commits.

This commit therefore instead uses "git show --oneline --no-patch HEAD",
which provides a short SHA-1, but also the names of any branches and
the commit's title.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>