Fix submission of Dataflow jobs

[damccorm]

Today, if you try to submit dataflow jobs with a mix of normal pipeline options and dataflow pipeline options, it does not get submitted correctly.

This is because cfg.command is quoted, so the final command ends up looking like this after adding dataflow_flags:

'
    python3 -m apache_beam.examples.wordcount             --input=gs://dataflow-samples/shakespeare/kinglear.txt         --output=gs://ttl-30d-us-central2/axlearn/users/remyw/dataflow/wordcount' --dataflow_service_options=enable_google_cloud_heap_sampling --dataflow_service_options=enable_secure_boot --experiments=use_network_tags=allow-internet-egress --experiments=use_runner_v2 --machine_type=n2-standard-8 --no_use_public_ips --project=abc --region=us-central1 --runner=DataflowRunner --sdk_container_image=my_container

Note the leading quote as well as the trailing quote after output=gs://ttl-30d-us-central2/axlearn/users/remyw/dataflow/wordcount'

This breaks the processing of this command, and all the subsequent dataflow_flags are ignored, so it gets run locally instead of on Dataflow.

To fix this, we just need to strip the quotes around cfg.command before adding it to our full command.

[markblee]

Thanks! cc @zhiyun

[damccorm]

Thanks! I reformatted to fix the precommit check since it looks like it was failing