[BUG] push sometimes omits status table when remote dies

If I run t5504 under heavy load, it sometimes fails tests 8 and 9, which
make a broken push to the remote. The failure looks like this:

    expecting success: 
            rm -rf dst &&
            git init dst &&
            (
                    cd dst &&
                    git config transfer.fsckobjects true
            ) &&
            test_must_fail git push --porcelain dst master:refs/heads/test >act &&
            test_cmp exp act
    
    Initialized empty Git repository in /var/ram/git-stress/root-13/trash directory.t5504-fetch-receive-strict/dst/.git/
    remote: fatal: object of unexpected type        
    error: failed to push some refs to 'dst'
    --- exp 2017-01-07 08:44:24.465771756 +0000
    +++ act 2017-01-07 08:44:24.493771755 +0000
    @@ -1,2 +0,0 @@
    -To dst
    -!      refs/heads/master:refs/heads/test       [remote rejected] (unpacker error)
    not ok 9 - push with transfer.fsckobjects

So it looks like we correctly fail the push, but the expected porcelain
output is missing. I'm _guessing_ what happens is that the local
git-push sees SIGPIPE writing to the remote side, and dies before it
gets a chance to write the message.

I'm not sure if this is something we should be fixing, or if the test is
simply a bit flaky (and we should work around it).

-Peff