cloud/bigquery: Add a readQuery method for fetching the results of a query.
cloud/bigquery: Add a readQuery method for fetching the results of a
query.

Change-Id: Iba6bb7fb5dd6b30221947533ea3e68d2e9147281

googleapis/google-cloud-go,hsinhoyeh/gcloud-golang,hsinhoyeh/gcloud-golang,blowmage/gcloud-golang,ptomasroos/gcloud-golang,googleapis/google-cloud-go,ptomasroos/gcloud-golang,googleapis/google-cloud-go,Maksadbek/gcloud-golang,googleapis/google-cloud-go,roth1002/gcloud-golang,blowmage/gcloud-golang,michael-grosshans/google-cloud-go,Maksadbek/gcloud-golang,michael-grosshans/google-cloud-go,roth1002/gcloud-golang