t3311: use test_commit_bulk

One of the tests in t3311 creates 300 commits by running "test_commit"
in a loop. This requires 900 processes. Instead, we can use
test_commit_bulk to do it with only four. This improves the runtime of
the script from:

  Benchmark #1: ./t3311-notes-merge-fanout.sh --root=/var/ram/git-tests
    Time (mean ± σ):      5.821 s ±  0.691 s    [User: 3.146 s, System: 2.782 s]
    Range (min … max):    4.783 s …  6.841 s    10 runs

to:

  Benchmark #1: ./t3311-notes-merge-fanout.sh --root=/var/ram/git-tests
    Time (mean ± σ):      1.743 s ±  0.116 s    [User: 1.144 s, System: 0.691 s]
    Range (min … max):    1.629 s …  1.994 s    10 runs

for an average speedup of over 70%.

Unfortunately we still have to run 300 instances of "git notes add",
since the point is to test the fanout that comes from adding notes one
by one.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t3311-notes-merge-fanout.sh

@@ -114,12 +114,12 @@ cp expect_log_x expect_log_y
 test_expect_success 'Add a few hundred commits w/notes to trigger fanout (x -> y)' '
 	git update-ref refs/notes/y refs/notes/x &&
 	git config core.notesRef refs/notes/y &&
-	i=5 &&
-	while test $i -lt $num
+	test_commit_bulk --start=6 --id=commit $((num - 5)) &&
+	i=0 &&
+	while test $i -lt $((num - 5))
 	do
-		i=$(($i + 1)) &&
-		test_commit "commit$i" >/dev/null &&
-		git notes add -m "notes for commit$i" || return 1
+		git notes add -m "notes for commit$i" HEAD~$i || return 1
+		i=$((i + 1))
 	done &&
 	test "$(git rev-parse refs/notes/y)" != "$(git rev-parse refs/notes/x)" &&
 	# Expected number of commits and notes