Fix "list comprehension redefines 'x'" warnings from pyflakes

  $ git ls-files | grep py$ | xargs pyflakes
  subcmds/stage.py:101: list comprehension redefines 'p' from line 63
  subcmds/sync.py:784: list comprehension redefines 'p' from line 664
  subcmds/upload.py:467: list comprehension redefines 'avail' from line 454

Change-Id: Ia65d1a72ed185ab3357e1a91ed4450c719e75a7c
diff --git a/subcmds/stage.py b/subcmds/stage.py
index 2884976..9d35426 100644
--- a/subcmds/stage.py
+++ b/subcmds/stage.py
@@ -60,8 +60,8 @@
       out.nl()
 
       for i in range(len(all_projects)):
-        p = all_projects[i]
-        out.write('%3d:    %s', i + 1, p.relpath + '/')
+        project = all_projects[i]
+        out.write('%3d:    %s', i + 1, project.relpath + '/')
         out.nl()
       out.nl()