add "ok=sigpipe" to test_must_fail and use it to fix flaky tests

t5516 "75 - deny fetch unreachable SHA1, allowtipsha1inwant=true" is
flaky in the following case:
1. remote upload-pack finds out "not our ref"
2. remote sends a response and closes the pipe
3. fetch-pack still tries to write commands to the remote upload-pack
4. write call in wrapper.c dies with SIGPIPE

The test is flaky because the sending fetch-pack may or may
not have finished writing its output by step (3). If it did,
then we see a closed pipe on the next read() call. If it
didn't, then we get the SIGPIPE from step (4) above. Both
are fine, but the latter fools test_must_fail.

t5504 "9 - push with transfer.fsckobjects" is flaky, too, and returns
SIGPIPE once in a while. I had to remove the final "To dst..." output
check because there is no output if the process dies with SIGPIPE.

Accept such a death-with-sigpipe also as OK when we are expecting a
failure.

Signed-off-by: Lars Schneider <larsxschneider@gmail.com>
Signed-off-by: Jeff King <peff@peff.net>

t/t5504-fetch-receive-strict.sh

@@ -100,7 +100,7 @@ test_expect_success 'push with receive.fsckobjects' '
 		git config receive.fsckobjects true &&
 		git config transfer.fsckobjects false
 	) &&
-	test_must_fail git push --porcelain dst master:refs/heads/test >act &&
+	test_must_fail ok=sigpipe git push --porcelain dst master:refs/heads/test >act &&
 	test_cmp exp act
 '
 
@@ -111,8 +111,7 @@ test_expect_success 'push with transfer.fsckobjects' '
 		cd dst &&
 		git config transfer.fsckobjects true
 	) &&
-	test_must_fail git push --porcelain dst master:refs/heads/test >act &&
-	test_cmp exp act
+	test_must_fail ok=sigpipe git push --porcelain dst master:refs/heads/test >act
 '
 
 cat >bogus-commit <<\EOF

t/t5516-fetch-push.sh

@@ -1162,15 +1162,15 @@ do
 		mk_empty shallow &&
 		(
 			cd shallow &&
-			test_must_fail git fetch ../testrepo/.git $SHA1_3 &&
-			test_must_fail git fetch ../testrepo/.git $SHA1_1 &&
+			test_must_fail ok=sigpipe git fetch ../testrepo/.git $SHA1_3 &&
+			test_must_fail ok=sigpipe git fetch ../testrepo/.git $SHA1_1 &&
 			git --git-dir=../testrepo/.git config uploadpack.allowreachablesha1inwant true &&
 			git fetch ../testrepo/.git $SHA1_1 &&
 			git cat-file commit $SHA1_1 &&
 			test_must_fail git cat-file commit $SHA1_2 &&
 			git fetch ../testrepo/.git $SHA1_2 &&
 			git cat-file commit $SHA1_2 &&
-			test_must_fail git fetch ../testrepo/.git $SHA1_3
+			test_must_fail ok=sigpipe git fetch ../testrepo/.git $SHA1_3
 		)
 	'
 done

t/test-lib-functions.sh

@@ -612,6 +612,9 @@ test_must_fail () {
 	then
 		echo >&2 "test_must_fail: command succeeded: $*"
 		return 1
+	elif test $exit_code -eq 141 && list_contains "$_test_ok" sigpipe
+	then
+		return 0
 	elif test $exit_code -gt 129 && test $exit_code -le 192
 	then
 		echo >&2 "test_must_fail: died by signal: $*"