Fix Spring Boot based Hazelcast samples

[vpavic]

There are several things wrong with the Spring Boot based Hazelcast samples:

• configurations declare beans named clientConfig implying the use of Hazelcast in a client-server topology, while the actual type is com.hazelcast.config.Config which means the embedded server topology is used (coupled with this the original, Hazelcast 3.x based sample, declares the dependency on hazelcast-client)
• tests configure Hazelcast containers which are not needed, because as explained above the sample actually uses the embedded server topology - additionally these containers use latest tag which makes the build non-reproducible