COM_CHANGE_USER and COM_RESET_CONNECTION commands cause
THD::cleanup() to be called in the middle of command handling.
This causes wsrep client_state sanity checks to fail.

As a fix, temporarily close wsrep client_state before THD::change_user()
is called when handling COM_CHANGE_USER and COM_RESET_CONNECTION,
and restore the state after THD::change_user() returns.

This commit also updates wsrep-lib to version which removes
exception usage in wsrep client_state sanity checks.