[FLINK-17230] Fix incorrect returned address of Endpoint for external Service of ClusterIP type

[zhengcanbin]

What is the purpose of the change

At the moment, when external Service is set to ClusterIP, we return ${internal-service-name} + "." + nameSpace as the address of the Endpoint, which could be problematic since we don't create the internal service in ZooKeeper based HA setups. According to FLINK-16602, we always use external Service for rest communication so that this PR returns ${external-service-name} + "." + nameSpace as Endpoint's address instead.

Brief change log

• Fix incorrect returned address of Endpoint for the external Service of ClusterIP type
• Port KubernetesUtils.getInternalServiceName to InternalServiceDecorator
• Port KubernetesUtils.getExternalServiceName to ExternalServiceDecorator
• Fix code style

Verifying this change

This change hardens Fabric8FlinkKubeClientTest#testClusterIPService to add a test branch for Endpoint's address.

Does this pull request potentially affect one of the following parts:

• Dependencies (does it add or upgrade a dependency): (no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (no)
• The serializers: (no)
• The runtime per-record code paths (performance sensitive): (no)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Kubernetes/Yarn/Mesos, ZooKeeper: (no)
• The S3 file system connector: (no)

Documentation

• Does this pull request introduce a new feature? (no)
• If yes, how is the feature documented? (not applicable)

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Last check on commit 689aafe (Fri Oct 16 10:54:39 UTC 2020)

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[zhengcanbin]

cc @tisonkun. Could you help take a look?

[wangyang0918]

Thanks for the changes. LGTM. +1 for merging.