Running the test suite in parallel causes flaky test behavior

[enter-github-username]

Running the test suite in parallel (using make -j16 check) causes tests to randomly fail.

The log files of the failing tests contain this error:

event.tst: tester.c:79: tester_create: Assertion `bind(t->pfd[FD_LISTEN].fd, (struct sockaddr*)&addr, len) == 0' failed.
FAIL event.tst (exit status: 134)

As far as I could debug the issue, this may be caused by multiple tests trying to bind to the same unix socket /tmp/test.vici, as defined in tester_create, line 64. A possible solution might be to use a different unix socket per test.