[RLlib] Fix large batch size for synchronous algos after EnvRunner failures.

[sven1977]

Fix large batch size for synchronous algos after EnvRunner failures.

• Make sure the to-be-collected batch size in a call to synchronous_parallel_sample are not exceeding too much the desired batch size only b/c of an EnvRunner failure and a repetition of the sample() call to all still-healthy remaining workers.
• Enhance node-failure tests and cover new API stack.

Why are these changes needed?

Related issue number

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[simonsays1980]

LGTM. Tricky situation.

[simonsays1980]

Nice!