Allow dot in token names

A year or two ago, with #208 a change was incorporated to enforce more strict naming rules. We often use FQDNs as tokens, eg for host/network definitions. Since this change that yields a large amount of warnings.

Would it be acceptable to also permit dots in token names? I haven't seen any problems yet when I locally change the token_re in L134 in naming.py, but maybe there's a downside to this that I don't understand yet.

[1] https://github.com/google/capirca/blob/4207b88d92beefb586b6214b6c13048df8084466/capirca/lib/naming.py#L134