t7102 (reset): don't hardcode SHA-1 in expected outputs

The expected SHA-1 digests are always available in variables. Use
them instead of hardcoding.

Signed-off-by: Alexey Shumkin <Alex.Crezoff@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t7102-reset.sh

@@ -192,7 +192,8 @@ test_expect_success \
 	'changing files and redo the last commit should succeed' '
 	echo "3rd line 2nd file" >>secondfile &&
 	git commit -a -C ORIG_HEAD &&
-	check_changes 3d3b7be011a58ca0c179ae45d94e6c83c0b0cd0d &&
+	head4=$(git rev-parse --verify HEAD) &&
+	check_changes $head4 &&
 	test "$(git rev-parse ORIG_HEAD)" = \
 			$head5
 '
@@ -211,7 +212,7 @@ test_expect_success \
 	git reset --hard HEAD~2 &&
 	check_changes ddaefe00f1da16864591c61fdc7adb5d7cd6b74e &&
 	test "$(git rev-parse ORIG_HEAD)" = \
-			3d3b7be011a58ca0c179ae45d94e6c83c0b0cd0d
+			$head4
 '
 
 >.diff_expect
@@ -326,10 +327,11 @@ test_expect_success '--hard reset to HEAD should clear a failed merge' '
 	git checkout branch2 &&
 	echo "3rd line in branch2" >>secondfile &&
 	git commit -a -m "change in branch2" &&
+	head3=$(git rev-parse --verify HEAD) &&
 
 	test_must_fail git pull . branch1 &&
 	git reset --hard &&
-	check_changes 77abb337073fb4369a7ad69ff6f5ec0e4d6b54bb
+	check_changes $head3
 '
 
 >.diff_expect