qemuxml2argvtest: Set timezone

With my recent work on the test, both time() and localtime() are used.
While mocking the former one, we get predictable result for UTC. But
since the latter function uses timezone to get local time, the result of
localtime() is not so predictive. Therefore, we must set the TZ variable
at the beginning of the test. To be able to catch some things that work
just by a blind chance, I'm choosing a virtual timezone that (hopefully)
no libvirt developer resides in.

tests/qemuxml2argvdata/qemuxml2argv-clock-localtime-basis-localtime.args

 LC_ALL=C PATH=/bin HOME=/home/test USER=test LOGNAME=test QEMU_AUDIO_DRV=none \
 /usr/bin/qemu -S -M pc -m 214 -smp 1 -nographic \
--monitor unix:/tmp/test-monitor,server,nowait -rtc base=2009-02-14T01:31:30 \
+-monitor unix:/tmp/test-monitor,server,nowait -rtc base=2009-02-14T00:01:30 \
 -no-acpi -boot c -usb -hda /dev/HostVG/QEMUGuest1 -net none -serial none \
 -parallel none

tests/qemuxml2argvtest.c

@@ -486,6 +486,16 @@ mymain(void)
     if (!abs_top_srcdir)
         abs_top_srcdir = abs_srcdir "/..";
 
+    /* Set the timezone because we are mocking the time() function.
+     * If we don't do that, then localtime() may return unpredictable
+     * results. In order to detect things that just work by a blind
+     * chance, we need to set an virtual timezone that no libvirt
+     * developer resides in. */
+    if (setenv("TZ", "VIR00:30", 1) < 0) {
+        perror("setenv");
+        return EXIT_FAILURE;
+    }
+
     driver.config = virQEMUDriverConfigNew(false);
     VIR_FREE(driver.config->spiceListen);
     VIR_FREE(driver.config->vncListen);