[Versioning] Mechanism to select command interface depending on API profile

[tjprescott]

Unresolved issue from PR #2526.

We should investigate having a way of defining and easily getting method signatures for different api versions. Something like:

storage_account_create_sig = {
  'profile1': (resource_group_name, account_name, location, account_type, tags=None),
  'profile2': (resource_group_name, account_name, location, sku, kind, encryption=None, access_tier=None, tags=None)
}

Then you have a way of getting an API specific signature for reflecting on parameters and so forth and you can call into a common implementation method by treating those signatures as kwargs.