When running the tests with atf-run the directory we are running in is
drwx------ so when we change to a different user, we can't find the socket
we created.

Make a directory and put the socket in there. Of course now atf can't
record its results as a different user, but that is not fatal.

tc-se:FATAL ERROR: Cannot create results file '/tmp/atf-run.9vOjFd/tcr': \
Permission denied

(christos)