Use COM_RESET_CONNECTION for MariaDB >= 10.2.4

[bgrainger]

COM_RESET_CONNECTION is supported in MariaDB starting in v10.2.4: https://mariadb.com/kb/en/library/com_reset_connection/

[MosheL]

it can solve the #612 ?

[bgrainger]

Unsure, as we don't yet know the cause of #612. This is just taking advantage of a possibly-faster way to reset pooled connections.

[MosheL]

It will be faster. I was found the old connection reset method can take a ~ 20ms sometimes.

Thanks for all.

[bgrainger]

Added in 0.50.0.