bigquery: add autodetect support to load job
bigquery: add autodetect support to load job

Change-Id: I6983f0d518539fc6484697c345a3109e526b077c
Reviewed-on: https://code-review.googlesource.com/9971
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

michael-grosshans/google-cloud-go,michael-grosshans/google-cloud-go