[beam_PostCommit_Python_VR_Spark ] Multiple tests failing due to coders.

• [Jenkins Job|https://builds.apache.org/job/beam_PostCommit_Python_VR_Spark/719/]

Initial investigation:

Multiple tests failing to set proper coder
RuntimeError: Pipeline test_pardo_windowed_side_inputs_1566389313.07_875931ef-c02f-481c-89a2-2d9376c41ecc failed in state FAILED: java.lang.ClassCastException: org.apache.beam.sdk.coders.LengthPrefixCoder cannot be cast to org.apache.beam.sdk.coders.KvCoder

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