Add support for building with Bazel

This change adds support for in Gerrit tree and standalone Bazel build
modes, using bazlets.

To build a single plugin, run:

  $ bazel build example-simpleSshCommand
  INFO: Found 1 target...
  Target //example-simpleSshCommand:example-simpleSshCommand up-to-date:
  INFO: Elapsed time: 0.171s, Critical Path: 0.07s

To build all plugins at once, run:

  $ bazel build :all
  INFO: Found 1 target...
  Target //:all up-to-date:
  INFO: Elapsed time: 0.326s, Critical Path: 0.21s
  $ unzip -t
    Archive:  bazel-genfiles/
    testing: example-simpleSshCommand.jar   OK

Change-Id: I5ec70eec2492e1d2bd3e968135ba8206abf82c22
10 files changed