test-logging: don't hard-code paths in /tmp

Since f6880b7f [qemu-log: support simple pid substitution for logs],
test-logging creates files with hard-coded names in /tmp. In the best
case, this prevents multiple developers from running "make check" on
the same machine. In the worst case, it allows for symlink attacks,
enabling an attacker to overwrite files that are writable to the
developer running "make check".

Instead of hard-coding the paths, create a temporary directory using
g_dir_make_tmp() and clean it up afterwards.

Fixes: f6880b7f ("qemu-log: support simple pid substitution for logs")
Signed-off-by: Sascha Silbe <silbe@linux.vnet.ibm.com>
Message-id: 1471545963-11720-3-git-send-email-silbe@linux.vnet.ibm.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
