bigtable/bttest: fix package name in sample code
bigtable/bttest: fix package name in sample code

example was using outdated package name for options

Change-Id: I890188b53d610d9e34c48dcf67cbbf5b2a2631c5
Reviewed-on: https://code-review.googlesource.com/7470
Reviewed-by: Jonathan Amsterdam <e3d3698b2ccd5955e4adf250d0785062d0f9018b@google.com>

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