MySQL: add utf8mb4 charsets

Change-Id: I7dfda411ed1d91e9eea43a1eb0cbc70807fedfbb
Reviewed-on: https://code.wireshark.org/review/3451
Reviewed-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Reviewed-by: Anders Broman <a.broman58@gmail.com>