t9300: use $ZERO_OID instead of hard-coded object ID

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reviewed-by: Eric Sunshine <sunshine@sunshineco.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

t/t9300-fast-import.sh

@@ -92,7 +92,7 @@ test_expect_success 'A: create pack from stdin' '
 	EOF
 
 	reset refs/tags/to-be-deleted
-	from 0000000000000000000000000000000000000000
+	from $ZERO_OID
 
 	tag nested
 	mark :6
@@ -102,7 +102,7 @@ test_expect_success 'A: create pack from stdin' '
 	EOF
 
 	reset refs/tags/nested
-	from 0000000000000000000000000000000000000000
+	from $ZERO_OID
 
 	tag nested
 	mark :7
@@ -286,7 +286,7 @@ test_expect_success 'A: verify pack' '
 test_expect_success 'A: verify diff' '
 	copy=$(git rev-parse --verify master:file2) &&
 	cat >expect <<-EOF &&
-	:000000 100755 0000000000000000000000000000000000000000 $copy A	copy-of-file2
+	:000000 100755 $ZERO_OID $copy A	copy-of-file2
 	EOF
 	git diff-tree -M -r master verify--import-marks >actual &&
 	compare_diff_raw expect actual &&
@@ -365,7 +365,7 @@ test_expect_success 'B: fail on invalid blob sha1' '
 	COMMIT
 
 	from refs/heads/master
-	M 755 0000000000000000000000000000000000000001 zero1
+	M 755 $(echo $ZERO_OID | sed -e "s/0$/1/") zero1
 
 	INPUT_END
 
@@ -620,8 +620,8 @@ test_expect_success 'D: validate new files added' '
 	f5id=$(echo "$file5_data" | git hash-object --stdin) &&
 	f6id=$(echo "$file6_data" | git hash-object --stdin) &&
 	cat >expect <<-EOF &&
-	:000000 100755 0000000000000000000000000000000000000000 $f6id A	newdir/exec.sh
-	:000000 100644 0000000000000000000000000000000000000000 $f5id A	newdir/interesting
+	:000000 100755 $ZERO_OID $f6id A	newdir/exec.sh
+	:000000 100644 $ZERO_OID $f5id A	newdir/interesting
 	EOF
 	git diff-tree -M -r branch^ branch >actual &&
 	compare_diff_raw expect actual
@@ -2733,7 +2733,7 @@ test_expect_success 'R: corrupt lines do not mess marks file' '
 	rm -f io.marks &&
 	blob=$(echo hi | git hash-object --stdin) &&
 	cat >expect <<-EOF &&
-	:3 0000000000000000000000000000000000000000
+	:3 $ZERO_OID
 	:1 $blob
 	:2 $blob
 	EOF
@@ -3084,7 +3084,7 @@ test_expect_success 'T: delete branch' '
 	git branch to-delete &&
 	git fast-import <<-EOF &&
 	reset refs/heads/to-delete
-	from 0000000000000000000000000000000000000000
+	from $ZERO_OID
 	EOF
 	test_must_fail git rev-parse --verify refs/heads/to-delete
 '