tests/kvm: Create the status tempfile in the build dir
mktemp can create a tempfile relative to a directory passed in via -p. It also uses the $TMPDIR variable for the same purpose. When the template is specified via -t, $TMPDIR takes precedence over -p. When the template is specified via a positional argument, -p takes precedence.
Since fec38819 $TMPDIR is set via the dbus runner which took precedence.
virtme-ng doesn't seem to share /tmp with the host system which results in the exit status from the test in the VM not propagating back to the test harness.
Fix that by making sure we always create the tempfile for the result in the build directory.