Update Mockito support so that AOP Proxies automatically get additional
`Advice` that allows them to work with Mockito. Prior to this commit a
call to `verify` would fail because exiting AOP advice would confuse
Mockito and an `UnfinishedVerificationException` would be thrown.

The `MockitoAopProxyTargetInterceptor` works by detecting calls to a
mock that have been proceeded by `verify()` and bypassing AOP to
directly call the mock.

The order that `@SpyBean` creation occurs has also been updated to
ensure that that the spy is created before AOP advice is applied.
Without this, the creation of a spy would fail because Mockito copies
'state' to the newly created spied instance. Unfortunately, in the case
of AOP proxies, 'state' includes cglib interceptor fields. This means
that Mockito's own interceptors are clobbered by Spring's AOP
interceptors.

Fixes gh-5837