Don't raise MySQL 2013 'Lost connection' errors

Closes-bug: #1276510

Although this code error is part of the `ping_listener` tests, it was
missing from the list of known - and ignored - connection errors.

The code error 2013 refers to a connection lost during a query, see:
https://dev.mysql.com/doc/refman/5.0/en/error-messages-client.html#error_cr_server_lost

Without this error code, the session won't try to reconnect to mysql,
which makes `max_retries` useless.

Change-Id: I57ac5a28f618b748f2c5a7657cc003bb8f2c0146

Not-in-upstream: true
Partial-rally-bug: DE770
Upstream-review: https://review.openstack.org/#/c/73793/
Merge pull request #29 from CiscoSystems/bugs/1276510

Don't raise MySQL 2013 'Lost connection' errors
Merge remote-tracking branch 'origin/cis-havana-staging' into cis-havana