INT-3321: Remove `powermock` Dependency

JIRA: https://jira.spring.io/browse/INT-3321

Refactor `StoredProcExecutorTests` just to use Mockito

INT-3321 Polishing

Mock the operations cache loader; remove static method.
INT-3324: Simple refactoring to `Routers`

JIRA: https://jira.spring.io/browse/INT-3324

* Move `private` `ExpressionControlBusFactoryBean$ControlBusMethodFilter` class
to the `org.springframework.integration.expression.ControlBusMethodFilter`
to make it as convenient to use from JavaConfig