[FLINK-12571][network] Make NetworkEnvironment#start() return the binded data port

[zhijiangW]

What is the purpose of the change

NetworkEnvironment#getConnectionManager is currently used for getting binded data port from ConnectionManager. Considering the general shuffle service architecture, the internal ConnectionManager in NetworkEnvironment should not be exposed to outsides. We could make ShuffleService#start return the binded data port directly if exists, then for other cases it could return a default int value which seems no harm.

Brief change log

• Make ConnectionManager#start return binded data port.
• Make NetworkEnvironment#start return binded data port
• Return legacy getter method in NettyServer
• Refactor the process in TaskManagerServices

Verifying this change

This change is a trivial rework / code cleanup without any test coverage.

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

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API, i.e., is any changed class annotated with @Public(Evolving): (yes / no)
• The serializers: (yes / no / don't know)
• The runtime per-record code paths (performance sensitive): (yes / no / don't know)
• Anything that affects deployment or recovery: JobManager (and its components), Checkpointing, Yarn/Mesos, ZooKeeper: (yes / no / don't know)
• The S3 file system connector: (yes / no / don't know)

Documentation

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

[zhijiangW]

@flinkbot attention @azagrebin

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[azagrebin]

Thanks @zhijiangW ! LGTM 👍
I think we just need a doc comment about the returned port.

[zhijiangW]

Thanks for reviews @azagrebin !

I pushed the fixup commit for adding doc comments and also another hotfix commit for removing legacy TaskEventDispatcher from NetworkEnvironment.

[pnowojski]

LGTM :) I will merge with green travis. Can you ping me once it's green?

[zhijiangW]

Thanks for reviews @pnowojski . It is already green.

[GJL]

Merging.