springboot mybatis配置多数据源的时候，报错：There is a circular dependency between 7 beans in the application context: xxx
经查，这是mybatis-spring的bug，延迟加载问题:https://github.com/mybatis/spring/issues/58
问题复现的版本组合是：
spring-boot-starter-parent 1.4.1.RELEASE
mybatis 3.2.8
mybatis-spring 1.3.0
问题解决：
mybatis-spring 降到 1.2.2