Fix minor python code style issues

Fix some minor issues that were reported by pyflakes and pylint.

- Rename arguments to prevent redefinition of built-in 'dir'
- Rename method call to prevent redefinition of built-in 'help'
- Remove unused imports
- Prefix unused variable with underscore to prevent warning

Change-Id: Ia9e21c0f1a69af43f6e4566be46c31bdda540d2f

tools/pack_war.py

@@ -15,7 +15,7 @@
 
 from __future__ import print_function
 from optparse import OptionParser
-from os import getcwd, chdir, makedirs, path, symlink
+from os import chdir, makedirs, path, symlink
 from subprocess import check_call, check_output
 import sys