[rllib] support running older version tensorflow(version < 1.5.0)

[adoda]

support run rllib's examples with older version tensorflow(version < 1.5.0)

What do these changes do?

support run the rllib's examples with tensorflow (version < 1.5.0)

• tf.boolean_mask only support tf.bool when tf version < 1.5.0

• tf.variable_scope support auxiliary_name_scope when tf version >= 1.5.0

Related issue number

#3570

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[richardliaw]

We shouldn't clutter the example but the rest of changes look fine to me

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[adoda]

@richardliaw updated

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[adoda]

jenkins, retest this please

[adoda]

unrelated error @richardliaw

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[adoda]

Could anybody help for this commit? @ericl @richardliaw

[richardliaw]

Test failures look unrelated - sorry for the delay!