Allow the Rally host to be specified through a command line switch.

Not all users of rally use rally1.rallydev.com. I changed the code to allow the Rally host to be configured through a command line option.

I decided not to use a config file property, because most of the time people will want to use rally1.rallydev.com. But... at Rally we have tests systems that we sometimes want to access with ralio. A command line option seemed like the best choice.