Reset database to guarantee the proper functionality of tests

[Wang-Benjamin]

Similar to #941 and #942, the following tests are also affected by polluted database when the execution order of tests changes.

tk.mybatis.mapper.test.country.TestSelect.testAllColumns
tk.mybatis.mapper.test.country.TestSelect.testDynamicSelect
tk.mybatis.mapper.test.country.TestSelect.testDynamicSelectAll
tk.mybatis.mapper.test.country.TestSelect.testDynamicSelectNotFoundKeyProperties
tk.mybatis.mapper.test.country.TestSelect.testDynamicSelectPage
tk.mybatis.mapper.test.country.TestUpdateByPrimaryKey.testDynamicUpdateByPrimaryKey
tk.mybatis.mapper.test.country.TestUpdateByPrimaryKey.testDynamicUpdateByPrimaryKeyNotFoundKeyProperties
tk.mybatis.mapper.test.country.TestUpdateByPrimaryKey.testUpdateByPrimaryKeyAndVersion
tk.mybatis.mapper.test.country.TestUpdateByPrimaryKeySelective.testDynamicUpdateByPrimaryKeySelective
tk.mybatis.mapper.test.country.TestUpdateByPrimaryKeySelective.testDynamicUpdateByPrimaryKeySelectiveNotFoundKeyProperties
tk.mybatis.mapper.test.example.TestDeleteByExample.testDeleteByExample
tk.mybatis.mapper.test.example.TestDeleteByExample.testDeleteByExample2
tk.mybatis.mapper.test.example.TestDeleteByExample.testDeleteByExample3

The fix to this issue is also the same, that is resetting/cleaning up the polluted database before running those tests.