Allow JAX coordinator to find the JobSet name.

[RoshaniN]

Fixes / Features

• CPU based workloads are not able to find the JAX coordinator. Reordering of env vars is needed following - https://github.com/google/xpk/pull/124 , as JOBSET_NAME comes through the env_vars and that is being used in the JAX_COORDINATOR.
• Thanks @raymondzouu for reporting this - https://screenshot.googleplex.com/7ZsGypAxqMqyuQq.

Testing / Documentation

Testing details.

• [ y] Tests pass
• [ y ] Appropriate changes to documentation are included in the PR