cbt: make it possible to combine read filters
cbt: make it possible to combine read filters

Change-Id: Ie8301e33deb22c0c37a43d5bf743a66ff17a9594
Reviewed-on: https://code-review.googlesource.com/27330
Reviewed-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Gary Elliott <d49662846a332c09d32ce16a761e8169b9defdba@google.com>

googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go,googleapis/google-cloud-go