all: changes from python 2 syntax to python3 and removing dead code

There were python 2 methods that are not used anymore so now
it's in python 3. Added helper fuctions so that the code is more clear

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/merge_requests/540

examples/python/dbus/update-secrets.py

@@ -13,8 +13,7 @@
 # values, and add them to the settings that we pass to Update().
 #
 
-import dbus
-import sys
+import dbus, sys
 
 bus = dbus.SystemBus()