Make '_configure_job_metadata' a free function.
Make '_configure_job_metadata' a free function.

Addresses:
https://github.com/GoogleCloudPlatform/gcloud-python/pull/1318#discussion_r48284147.

jgeewax/gcloud-python,daspecster/google-cloud-python,waprin/gcloud-python,tseaver/google-cloud-python,tartavull/google-cloud-python,tswast/google-cloud-python,jonparrott/gcloud-python,dhermes/gcloud-python,waprin/gcloud-python,VitalLabs/gcloud-python,jgeewax/gcloud-python,tartavull/google-cloud-python,calpeyser/google-cloud-python,dhermes/gcloud-python,quom/google-cloud-python,waprin/google-cloud-python,dhermes/google-cloud-python,tseaver/gcloud-python,elibixby/gcloud-python,googleapis/google-cloud-python,calpeyser/google-cloud-python,GoogleCloudPlatform/gcloud-python,elibixby/gcloud-python,tseaver/gcloud-python,tswast/google-cloud-python,waprin/google-cloud-python,GoogleCloudPlatform/gcloud-python,jonparrott/google-cloud-python,Fkawala/gcloud-python,jonparrott/google-cloud-python,daspecster/google-cloud-python,tseaver/google-cloud-python,dhermes/google-cloud-python,googleapis/google-cloud-python,jonparrott/gcloud-python,Fkawala/gcloud-python,tseaver/google-cloud-python,VitalLabs/gcloud-python,quom/google-cloud-python,dhermes/google-cloud-python,tswast/google-cloud-python