Support configuration databaseId.

[nieqiurong]

#911

[kazuki43zoo]

@nieqiurong Thank you for your contribution!
I will accept your changes, but I added a small comment, so please check it.

[coveralls]

coverage: 97.719% (+0.02%) from 97.703%
when pulling 6f90947 on nieqiurong:support_dataBaseId
into c8826e6 on mybatis:master.

[kazuki43zoo]

@nieqiurong If you have a time, please modify tests of MybatisPropertiesTest.

• Add assertion on testWithDefaultCoreConfiguration
• Add a property of databaseId and assertion on testWithCustomizeCoreConfiguration
• Remove the databaseId from https://github.com/mybatis/spring-boot-starter/blob/master/mybatis-spring-boot-autoconfigure/src/test/java/org/mybatis/spring/boot/autoconfigure/MybatisPropertiesTest.java#L249.

If you are busy, I will perform those.

[nieqiurong]

@nieqiurong If you have a time, please modify tests of MybatisPropertiesTest.

• Add assertion on testWithDefaultCoreConfiguration
• Add a property of databaseId and assertion on testWithCustomizeCoreConfiguration
• Remove the databaseId from https://github.com/mybatis/spring-boot-starter/blob/master/mybatis-spring-boot-autoconfigure/src/test/java/org/mybatis/spring/boot/autoconfigure/MybatisPropertiesTest.java#L249.

If you are busy, I will perform those.

Hi i'm done