Allow dots in VM names

Fixes: QubesOS/qubes-issues#8199

qubes/vm/__init__.py

@@ -53,7 +53,7 @@ def validate_name(holder, prop, value):
 
     # this regexp does not contain '+'; if it had it, we should specifically
     # disallow 'lost+found' #1440
-    if re.match(r"\A[a-zA-Z][a-zA-Z0-9_-]*\Z", value) is None:
+    if re.match(r"\A[a-zA-Z][a-zA-Z0-9_.-]*\Z", value) is None:
         if holder is not None and prop is not None:
             raise qubes.exc.QubesPropertyValueError(holder, prop, value,
                 '{} value contains illegal characters'.format(prop.__name__))