ui: use explicit None to get ui.formatted and ui.interactive

Summary:
This is subtle. `configbool` by default returns `False` for "unset"
configs. However, with `coreconfigitem(a, b, default=None)`,
`configbool(a, b)` will return `None`. I'm removing `coreconfigitem`s
so let's use explicit `None` for those tricky `configbool`s.

Reviewed By: muirdm

Differential Revision: D74336719

fbshipit-source-id: 048ca326ab3af378a31b79742d58a574bfe8302f

Author: quark-zju

eden/scm/sapling/ui.py

@@ -960,7 +960,7 @@ def interactive(self):
 
         This function refers to input only; for output, see `ui.formatted()'.
         """
-        i = self.configbool("ui", "interactive")
+        i = self.configbool("ui", "interactive", None)
         if i is None:
             # some environments replace stdin without implementing isatty
             # usually those are non-interactive
@@ -1005,7 +1005,7 @@ def formatted(self):
         if self.plain():
             return False
 
-        i = self.configbool("ui", "formatted")
+        i = self.configbool("ui", "formatted", None)
         if i is None:
             # some environments replace stdout without implementing isatty
             # usually those are non-interactive