[DO_NOT_MERGE] [origin-ui-180] rhc support for multiple servers

@liggitt 
This is the caveat of overriding global options instead of having an explicit 'discard' method: I have to reject values that were not explicitly provided through options in order to be able to have options that are optional (for example, --rhlogin is optional in the 'rhc server configure' command, if not provided I need to get nil instead of what's in express.conf or defaults).
Other than that works fine, no more discard_global_option.