Fix lint error about too many variables

Lint complains about too many variables in the CheckPrereq
method. While I think that this method/class would need
some refactoring in general, at least this patch makes lint
shut up for now.

Signed-off-by: Helga Velroyen <helgav@google.com>
Reviewed-by: Michele Tartara <mtartara@google.com>
Signed-off-by: Iustin Pop <iustin@google.com>