Bumping to 1.0.0-rc2, 0.15.0-beta, 0.15.0-alpha for release (googleap…

…is#1971)

Release 0.14.0; release 1.0.0-rc1 for google-cloud-core, google-cloud…

…-logging, google-cloud-storage, google-cloud-datastore

Updating version in README files. [ci skip]

Merge pull request googleapis#1885 from vam-google/master

Release 0.12.0

Updating version in README files. [ci skip]

Updating version in README files. [ci skip]

Updating version in README files. [ci skip]

Updating version in README files. [ci skip]

Release 0.9.4 (googleapis#1703)

Updating version in README files. [ci skip]