[maven-release-plugin] prepare release clouddocs-maven-plugin-1.15.0

Change-Id: I3ce2bae8c9bfab719948cf1771a59d1edbca7edb
[maven-release-plugin] prepare for next development iteration

Change-Id: Iffb4c00a640830f84ddd0cf3eac5e75692dc7f60