2to3: preparatory work for python 3

This patch for configshell-fb intend to ease compatibility with Python 3.

I ran `2to3` and selected the only fix named _except_ that we can apply right now because it is compatible with Python 2.7.

I did not apply the other fixes because I think they will break compatibility with Python 2.7. For configshell-fb, these fixes are:

 * basestring
 * dict
 * import
 * imports
 * raw_input
 * unicode
 * xrange
 * zip