Refactor common code for spring apps into spring-common

- Also change urls for service checks to <service>/url and <service>/check-access form
  (for example, datasource/url and datasource/check-access)
- Bump spring to 4.0.0.RC2

Note: to work around https://github.com/spring-projects/spring-boot/issues/170,
an empty controller was added to the Spring Boot CLI application.

[#62174332]
Merge 62174332-factor-out-spring-common to master

[Completes #62174332]