bigtable/bttest: Use binary searches for timestamp-based cell deletion.
bigtable/bttest: Use binary searches for timestamp-based cell deletion.

Change-Id: I3b50bc808160bba065e434df698aa17fc928a806

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