cloud: Add licence information to option.go
cloud: Add licence information to option.go

Change-Id: Iff48eda395e5ea69d865b05067b751db1111dc10

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