Make scalable application HA while application creation using RHC

- Run the following command to make an scalable application HA

   rhc app-create your-app-name cartridge-name -s -x
        OR
   rhc app-create your-app-name cartidge-name -s --make-ha

- Check if you have 2 HA-proxies on each of the 2 gears created by running the following command-

   rhc app-show your app name --gears

Bug - 1139374
Bugzilla Link- https://bugzilla.redhat.com/show_bug.cgi?id=1139374

Add testcase for -x/--make-ha

- Check if exception is raised  when there's any issue while making an application HA

- Check whether -x/--make-ha is allowed only if an app is made a scale one i.e if a -s option is passed before