tests: Ensure python tests exit with error on every exception

We ignored assertions happening on callbacks as they only raise
exceptions that does not stop the execution.

So ensure that this is happening in all the tests as synaptics was
doing already

tests/capture.py

@@ -1,10 +1,15 @@
 #!/usr/bin/python3
 
-import gi
-gi.require_version('FPrint', '2.0')
-from gi.repository import FPrint, GLib
 import cairo
 import sys
+import traceback
+import gi
+
+gi.require_version('FPrint', '2.0')
+from gi.repository import FPrint, GLib
+
+# Exit with error on any exception, included those happening in async callbacks
+sys.excepthook = lambda *args: (traceback.print_exception(*args), sys.exit(1))
 
 if len(sys.argv) != 2:
     print("Please specify exactly one argument, the output location for the capture image")