Breaking change - Push rightscale inputs deeper in server config.

Prior to this change, one would specify the server template inputs in a
rightscale server config like this:

    servers:
      my_rs_server:
        # other server attributes omitted for brevity
        provider: rightscale
        inputs:
          DOMAIN: foo.net
          SOME_OTHER_INPUT: blah blah

Provider-specific attributes needed to create/launch servers will now be
nested one level deeper in an attribute named after the provider.  With
this new structure, the corresponding configuration for the example
above would look like this:

    servers:
      my_rs_server:
        # other server attributes omitted for brevity
        provider: rightscale
        rightscale:
          inputs:
            DOMAIN: foo.net
            SOME_OTHER_INPUT: blah blah
Add provider_extras to rightscale server consul.

This new argument to the define_server() and create_server() methods
allows any rightscale-specific server attributes in the bang stack
config file to pass through to the rightscale api call while allowing
all the intermediate Bang code to just ignore the attributes.
Add a doc and example for rightscale