Fail to open file when multiple instance of a test run in parallel

[picojulien]

context

I have a non-deterministic test failure that I try to trigger by launching multiple instances of the same test in parallel.

bug

It used work well, but it now fails with

test_p2p_socket.exe: internal error, uncaught exception:
                     Unix.Unix_error(Unix.ENOENT, "open", "/home/julien/tezos/_build/_tests/tezos-p2p/p2p-connection..000.output")
                     Raised by primitive operation at file "src/alcotest/alcotest.ml", line 86, characters 24-74
                     Called from file "src/alcotest-engine/core.ml", line 292, characters 4-13
                     Called from file "src/alcotest-engine/monad.ml", line 68, characters 12-20
                     Called from file "src/alcotest-engine/core.ml", line 319, characters 4-103
                     Called from file "src/alcotest-engine/core.ml", line 465, characters 4-365
                     Called from file "src/alcotest-engine/cli.ml", line 117, characters 4-128
                     Called from file "cmdliner_term.ml", line 25, characters 19-24
                     Called from file "cmdliner.ml", line 117, characters 32-39

possible explanation

From what I'v seen, it's might be related to the fact that in core.ml the function redirect_test_output uses output_file with ~via_simlink:true.

Maybe the test tries to open the result file "p2p-connection..000.output" using the simlink "tezos-p2p", but an other test is concurrently moving the simlink to a new directory.

[picojulien]

Very dirty hack on https://github.com/picojulien/alcotest/commits/master fixed my problem.