logging: set client info header
logging: set client info header

Change-Id: I08295ae3dc373100b407867e8ca9c7901fb051de
Reviewed-on: https://code-review.googlesource.com/7221
Reviewed-by: Michael McGreevy <e70fec140fa6773c6cfd45cb9b436bd6334f4c24@golang.org>

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