Dataproc: fix client_info bug, update docstrings.

[dpebot]

This PR was generated using Autosynth. 🌈

Here's the log from Synthtool:

synthtool > Cloning googleapis. synthtool > Running generator for google/cloud/dataproc/artman_dataproc_v1beta2.yaml. synthtool > Ensuring dependencies. synthtool > Pulling artman image. synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/dataproc-v1beta2. synthtool > Replaced 'metadata_type=operations_pb2.ClusterOperationMetadata,' in google/cloud/dataproc_v1beta2/gapic/cluster_controller_client.py. synthtool > No replacements made in google/cloud/dataproc_v1beta2/gapic/cluster_controller_client.py for pattern \s+<strong>Note:</strong>.* (.* )+?.*types.FieldMask., maybe replacement is not longer needed? synthtool > Running generator for google/cloud/dataproc/artman_dataproc_v1.yaml. synthtool > Ensuring dependencies. synthtool > Pulling artman image. synthtool > Generated code into /home/kbuilder/.cache/synthtool/googleapis/artman-genfiles/python/dataproc-v1. synthtool > Replaced 'metadata_type=operations_pb2.ClusterOperationMetadata,' in google/cloud/dataproc_v1/gapic/cluster_controller_client.py. synthtool > No replacements made in google/cloud/dataproc_v1/gapic/cluster_controller_client.py for pattern \s+<strong>Note:</strong>.* (.* )+?.*types.FieldMask., maybe replacement is not longer needed? synthtool > Replaced '# Generated by the protocol buffer compiler. DO NOT EDIT!' in google/cloud/dataproc_v1beta2/proto/clusters_pb2.py. synthtool > Replaced ', and must\n\\s+conform to the following PCRE regular expression:(.*\n)+?.*No more than 32' in google/cloud/dataproc_v1beta2/proto/workflow_templates_pb2.py. synthtool > Replaced ', and must conform to\n\\s+the following regular expression:(.*\n)+?.* No more than' in google/cloud/dataproc_v1beta2/proto/workflow_templates_pb2.py. synthtool > No replacements made in google/cloud/dataproc_v1/gapic/cluster_controller_client.py for pattern } (\s+Similarly, to change the number of preemptible workers in a cluster to 5,), maybe replacement is not longer needed? synthtool > Cleaned up 0 temporary directories. 

[tseaver]

Includes codegen fix for #5710.