Feature:  run_locally now supports "echo: true" option.

I use run_locally to run acceptance tests before allowing a deploy.  Problem is, run_locally doesn't echo the rspec commands running, so there is no output for 3 minutes while my tests are running.  Would be much better if the "run_locally" command allowed real-time echo of my acceptance tests running so I can see what is going on.   This commit adds such a "echo: true" option.

Now, my acceptance test task looks like this:

  task :acceptance_test do
    begin
      run_locally "bundle exec rake spec", echo: true
    rescue => ex
      logger.important "Error:  #{ex.message}"
    end
    if $? != 0
      logger.important "Acceptance Tests FAILED!  Aborting..."
      exit
    else
      logger.info "Acceptance Tests PASSED."
    end
  end