Add support for wheezy in build_chroot.

* Run squeeze-specific install logic only when building squeeze
  * Collapse consecutive apt-get commands
* Add wheezy-specific install logic
  * Ask for python-pyinotify 0.9.4 to avoid py-apidoc failures
* Add generic setup logic

Commands inside the new case construct were not indented inside the
new case construct for reviewing convenience. This will be fixed in
the next patch. The changes allow "make commit-check" to run to completion
without errors inside the newly created chroot.

Signed-off-by: Santi Raffa <rsanti@google.com>
Signed-off-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>