Add Jenkins build support

[mynnx]

This adds a module similar to the BuildBot module, with tools for building via the Jenkins API. Here's an example of how it would be used:

jenkins = new Jenkins(stack.config.jenkins, baton.log);
  jenkins.ensureRevisionBuilt(stack.stackConfig.builder, args.revision, function(err, build) {
    if (err) {
      return callback(err);
    }

    if (!jenkins.isBuildSuccessful(build)) {
      buildStatus = util.format("ERROR: Build %s had status %s",
                                build.fullDisplayName,
                                build.result)
      return callback(new Error(buildStatus));
    }

    baton.build = build;
    callback(err, build);
  });

Due to a cookie bug in requests v2.2.5, I updated that module as well.