tests/9pfs: fix mkdir() being called twice

tests/9pfs: fix mkdir() being called twice

The 9p test cases use mkdtemp() to create a temporary directory for
running the 'local' 9p tests with real files/dirs. Unlike mktemp()
which only generates a unique file name, mkdtemp() also creates the
directory, therefore the subsequent mkdir() was wrong and caused
errors on some systems.

Signed-off-by: Christian Schoenebeck <qemu_oss@crudebyte.com>
Fixes: 136b7af2 (tests/9pfs: fix test dir for parallel tests)
Reported-by: Daniel P. Berrangé <berrange@redhat.com>
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/832
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Greg Kurz <Greg Kurz <groug@kaod.org>
Message-Id: <f6602123c6f7d0d593466231b04fba087817abbd.1642879848.git.qemu_oss@crudebyte.com>