Reset the database connection after MySQL bulk insert failure

After a bulk insert failure in MySQL (caused by servers not
allowing this by default) we fall back to a line by line insert.
However, using pymysql the failed insert causes the database
connection to get hung up.

This commit creates a new method to reset the connection and
calls it prior to starting the line by line insert.
Add a test for a database with bulk insert failures on MySQL
Explicitly resetting the database connection is unnecessary

Since it is a property it can simply be disconnected and will
automatically restablish itself when needed.
Merge pull request #133 from ethanwhite/mysql-bug

Reset the database connection after MySQL bulk insert failure