Add plugin configuration to maven-release-plugin
Merge pull request googleapis#934 from google/release-1.20.0 Release 1.20.0
api 1.16: Add plugin configuration to maven-release-plugin https://codereview.appspot.com/11616044/
[maven-release-plugin] prepare release 1.15.0-rc
[maven-release-plugin] prepare release 1.14.1-beta