tests: fix race condition in net-accept-connect based tests

Change all net-accept-connect based tests to use different unix domain
socket addresses, so that these tests could be safely run in parallel.

* tests/net-accept-connect.c: Parametrize unix domain socket address.
* tests/net-fd.test: Pass socket address to net-accept-connect.
* tests/net.test: Likewise.
* tests/unix-yy.test: Likewise.
* tests/unix-yy-accept.awk: Update regexps.
* tests/unix-yy-connect.awk: Likewise.
6 files changed