small improvements to solve_disambiguation.py

* run also on sites with dn_template not defined
* add tools.concat_options which is similar to textwrap.fill() but only
  adds a newline between two options (and not any space)
* replace `find` with `in`, which is prettier and faster:
 * http://stackoverflow.com/a/4901653
 * http://stackoverflow.com/a/18437853
* buffer the translated dn_template into dn_template_str once per site
* use dn_template_str[:-2] instead of dn_template_str[:4]
  to support floating-length templates

Bug: T78521
Change-Id: Iade765b402498876b8ea6ebbd31649f17c67f9eb
Merge "small improvements to solve_disambiguation.py"