Use Flyway to bind flyway.*

Since Flyway has bean properties (with getters and setters)
it can be used to bin directly to the Environment (instead of
copying all the properties into FlywayProperties).

Fixes gh-806

spring-boot-samples/spring-boot-sample-flyway/src/main/resources/application.properties

@@ -1,2 +1 @@
-spring.jpa.generate-ddl: false
 spring.jpa.hibernate.ddl-auto: validate