qemu: Increase guest startup timeout to 30 seconds

Currently the timeout for reading startup output is 3 seconds. If the
host is under any sort of load, we can easily trigger this. Lets bump
it to 30 seconds.

Since the polling loop checks to see if the process has died, we shouldn't
erroneously hit this timeout if qemu bombs (only if it is stuck in some
infinite loop).

src/qemu/qemu_driver.c

@@ -1541,7 +1541,7 @@ qemudWaitForMonitor(struct qemud_driver* driver,
 
     ret = qemudReadLogOutput(vm, logfd, buf, sizeof(buf),
                              qemudFindCharDevicePTYs,
-                             "console", 3);
+                             "console", 30);
     if (close(logfd) < 0) {
         char ebuf[4096];
         VIR_WARN(_("Unable to close logfile: %s"),