Add support  for rhc app make-ha

Currently when creating an ha application you have to do it via curl, for exemple

    $ rhc create-app testha ruby-1.9 -s
    Your application ‘testha’ is now available.

    $ curl -k -X POST https://broker.example.com/broker/rest/domains/test/applications/testha/events –user demo:password –data-urlencode event=make-ha

This pull request add support for `make-ha` in rhc

    $ rhc app make-ha -a testha