[FLINK-9326] TaskManagerOptions.NUM_TASK_SLOTS does not work for local/embedded mode

[yanghua]

What is the purpose of the change

This pull request fixed the num slot config value override error.

Brief change log

• fixed the num slot config value override error.

Verifying this change

This change is already covered by existing tests*.

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)

[yanghua]

cc @tillrohrmann

[yanghua]

cc @zentol @tzulitai if you have time, please review this PR, thanks~

[zentol]

this block can be simplified to:

numSlotsPerTaskManager = configuration.getInteger(TaskManagerOptions.NUM_TASK_SLOTS, jobGraph.getMaximumParallelism());

[yanghua]

@zentol does it need a new commit?

[yanghua]

cc @zentol

[zentol]

merging.