MySQL: Support authplugin and connattrs

Bug:10294

Signed-off-by: Alexis La Goutte <alexis.lagoutte@gmail.com>
Change-Id: I65ec69821fd562da8f873ae85b1846c79ab400d9
Reviewed-on: https://code.wireshark.org/review/3138
Reviewed-by: Daniël van Eeden <wireshark@myname.nl>
Reviewed-by: Evan Huus <eapache@gmail.com>