* Build role requires build target to be specified via a variable
* Ensure role checks for a specific version of Bazel and downloads
and installs if missing; defaults to v3.1.0 and downloading from
bazelbuild Github, but these can be overrriden using variables
* Also installs dependencies for Bazel; only supports Ubuntu/Debian
at present, but includes scope to extend for other platforms
* Includes test playbook and job
Change-Id: I83f198aaf20c2b3664bea6fc05edd3b4fca13a4f
ad7297199d