update bigtable protos

[Shawn Morel]

It looks like the bigtable-protos found here (https://github.com/GoogleCloudPlatform/cloud-bigtable-client/tree/master/bigtable-protos) contain changes not available yet in googleapis. Additionally, The bigtable-protos project copies a subset of the googleapis protos making building the full set of bigtable protos tedious if you also depend on other protos in googleapis.

Any chance the googleapis project could track the latest bigtable proto changes? Pulling and building just googleapis would be quite convenient.

thanks,

shawn