net: allow concurrent UNIX socket tests if TMPDIR is unique.
net: allow concurrent UNIX socket tests if TMPDIR is unique.

Only clever enough to allow concurrent stress testing.

R=mikioh.mikioh, rsc
CC=golang-dev
https://codereview.appspot.com/7703044

Committer: Russ Cox <5ad239cb8a44f659eaaee0aa1ea5b94947abe557@golang.org>

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