tests: Make meson be aware of the single python unit tests

Scan for the unit tests in virtual-image suite and handle them individually

tests/virtual-image.py

@@ -345,6 +345,6 @@ class VirtualImage(unittest.TestCase):
             ctx.iteration(True)
         assert(not self._verify_match)
 
-# avoid writing to stderr
-unittest.main(testRunner=unittest.TextTestRunner(stream=sys.stdout, verbosity=2))
-
+if __name__ == '__main__':
+    # avoid writing to stderr
+    unittest.main(testRunner=unittest.TextTestRunner(stream=sys.stdout, verbosity=2))