avoid negative variables

Trying to use booleans with names like "no_xxx" are hard to follow due
to the double negatives.  Invert all of them so we only have positive
meanings to follow.

Change-Id: Ifd37d0368f97034d94aa2cf38db52c723ac0c6ed
Reviewed-on: https://gerrit-review.googlesource.com/c/git-repo/+/255493
Tested-by: Mike Frysinger <vapier@google.com>
Reviewed-by: David Pursehouse <dpursehouse@collab.net>
diff --git a/subcmds/rebase.py b/subcmds/rebase.py
index eb92a3c..24d80bf 100644
--- a/subcmds/rebase.py
+++ b/subcmds/rebase.py
@@ -53,7 +53,7 @@
                  dest='force_rebase', action='store_true',
                  help='Pass --force-rebase to git rebase')
     p.add_option('--no-ff',
-                 dest='no_ff', action='store_true',
+                 dest='ff', default=True, action='store_false',
                  help='Pass --no-ff to git rebase')
     p.add_option('-q', '--quiet',
                  dest='quiet', action='store_true',
@@ -93,7 +93,7 @@
       common_args.append('--quiet')
     if opt.force_rebase:
       common_args.append('--force-rebase')
-    if opt.no_ff:
+    if not opt.ff:
       common_args.append('--no-ff')
     if opt.autosquash:
       common_args.append('--autosquash')