tests: gadget-zero: run against all attached targets

Less command line arguments, more automatic "do what I mean"

tests/gadget-zero/test_gadget0.py

@@ -10,6 +10,8 @@ import unittest
 VENDOR_ID=0xcafe
 PRODUCT_ID=0xcafe
 
+# you only need to worry about these if you are trying to explicitly test
+# a single target.  Normally, the test will autofind the attached target
 #DUT_SERIAL = "stm32f429i-disco"
 DUT_SERIAL = "stm32f4disco"
 #DUT_SERIAL = "stm32f103-generic"
@@ -385,5 +387,12 @@ class TestUnaligned(unittest.TestCase):
 if __name__ == "__main__":
     if len(sys.argv) > 1:
         DUT_SERIAL = sys.argv.pop()
-    print("Running tests for DUT: ", DUT_SERIAL)
-    unittest.main()
+        print("Running tests for DUT: ", DUT_SERIAL)
+        unittest.main()
+    else:
+        # scan for available and try them all!
+        devs = usb.core.find(idVendor=VENDOR_ID, idProduct=PRODUCT_ID, find_all=True)
+        for dev in devs:
+            DUT_SERIAL = dev.serial_number
+            print("Running tests for DUT: ", DUT_SERIAL)
+            unittest.main(exit=False)