DRILL-3791: MySQL tests for JDBC plugin
This commit adds integration tests for the JDBC plugin with MySQL. It
also refactors the existing Derby tests to have the same general pattern
as the MySQL tests: data is defined in an external .sql file and maven
is used to start/stop external resources for testing.
Add tests for ENUM and YEAR types.
Tests for the CLOB type with Derby.
This closes #251
