superproject: Provide accurate feedback for user choice

Currently the code would give a message that would appear like the user
have enrolled the experiment regardless of the actual choice. For users
who choose to not enroll in the experiment, we should give them
instructions to override (enable) superproject once instead of how to
disable it, which is what the code already behave.

Bug: [google internal] b/199167992
Change-Id: Iba3314cb510aedf024375a26baa8bc1d5e2846cf
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/317382
Tested-by: Xin Li <delphij@google.com>
Reviewed-by: Raman Tenneti <rtenneti@google.com>

git_superproject.py

@@ -369,9 +369,14 @@ def _UseSuperprojectFromConfiguration():
     if user_expiration is not None and (user_expiration <= 0 or user_expiration >= time_now):
       # TODO(b/190688390) - Remove prompt when we are comfortable with the new
       # default value.
-      print(('You are currently enrolled in Git submodules experiment '
-             '(go/android-submodules-quickstart).  Use --no-use-superproject '
-             'to override.\n'), file=sys.stderr)
+      if user_value:
+        print(('You are currently enrolled in Git submodules experiment '
+               '(go/android-submodules-quickstart).  Use --no-use-superproject '
+               'to override.\n'), file=sys.stderr)
+      else:
+        print(('You are not currently enrolled in Git submodules experiment '
+               '(go/android-submodules-quickstart).  Use --use-superproject '
+               'to override.\n'), file=sys.stderr)
     return user_value
 
   # We don't have an unexpired choice, ask for one.