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

[rdhallman]

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

[leehambley]

Can you rebase this against master and I'll merge it in?