qubes/tools: accept properties with '-'

'-' is invalid character in python identifier, so all the properties
have '_'. But in previous versions qvm-* tools accepted names with '-',
so lets not break this.

QubesOS/qubes-issues#2412

qubes/tools/qubes_prefs.py

@@ -87,6 +87,8 @@ def main(args=None):
                     name=prop.__name__, width=width, value=value))
 
         return 0
+    else:
+        args.property = args.property.replace('-', '_')
 
 
     if args.value is not None:

qubes/tools/qvm_prefs.py

@@ -91,6 +91,8 @@ def main(args=None):
                     name=prop.__name__, width=width, value=value))
 
         return 0
+    else:
+        args.property = args.property.replace('-', '_')
 
     if args.property not in [prop.__name__
                              for prop in args.domain.property_list()]: