re-support mysql-connector python

re-support mysql-connector python

Support has been re-added for the MySQL-Connector/Python DBAPI using the
``mysql+mysqlconnector://`` URL scheme.   The DBAPI now works against
modern MySQL versions as well as MariaDB versions (in the latter case it's
required to pass charset/collation explicitly).   Note however that
server side cursor support is disabled due to unresolved issues with this
driver.

note the 2.0 backport here necessarily needs to also backport some
of 49ce245998 to handle the mariadb database working under mysql
connector.

References: #12332
Change-Id: I81279478196e830d3c0d5f24ecb3fe2dc18d4ca6
(cherry picked from commit b056dd2c5ab71ce4143a95cd0fdd4a4190de19e6)