* [google-cloud-cpp] Consolidate all google-cloud* packages
Starting with the v1.14.0 release all google-cloud* packages and the
googleapis package are kept in a single repository and released
simultaneously.
* Update CI baseline.
google-cloud-cpp used to inherit failures from googleapis, which
indicates these are (probably) problems in the generated protobuf/grpc
code.
Update google-cloud-cpp-common to v0.21.0, google-cloud-cpp to v0.20.0,
and google-cloud-cpp-spanner to v0.9.0. These changes need to be atomic,
thus the single PR.
