Dataflow runner raises AssertionError if job takes > 50 seconds to go from PENDING to RUNNING

To reproduce:

• Try to run a Pipeline that takes longer than 50 seconds to go from JOB_STATE_PENDING to JOB_STATE_RUNNING using "with Pipeline() as pipeline:" (automatically executes pipeline.run().wait_until_finish() via Pipeline._exit_) on Dataflow.
• Your script will raise "AssertionError: Job did not reach to a terminal state after waiting indefinitely." (from https://github.com/apache/beam/blob/766a1dc5b6523a0b7a3ce0a9ab78901cf17c9013/sdks/python/apache_beam/runners/dataflow/dataflow_runner.py#L1152-L1153)

I think the issue is that the block at https://github.com/apache/beam/blob/766a1dc5b6523a0b7a3ce0a9ab78901cf17c9013/sdks/python/apache_beam/runners/dataflow/dataflow_runner.py#L147-L160 unintentionally exits if it takes > 50 seconds for a job to go from JOB_STATE_PENDING to JOB_STATE_RUNNING.