Client: Move LDAP token file from ~/.manager/token to ~/.atlantis/manager-tokens
Client: Support multiple tokens in LDAP cache.
Client: Wrap RPCClient to handle auth at that layer instead of at each call.
Client: Add dummyAuthArg, since auth can't be nil, but CallAuthed is setting it later.
Client: Use RPCClient CallAuthed for auth instead of loading on every single call.

This saves five lines in every authorized call, and will likely also make
multi-region easier.

The pattern of changes is easy to see with `git show --color-words=.`
Client: Label username/password as LDAP to avoid confusion.
Merge pull request #42 from ooyala/auth-in-rpc

Let's not have a bunch of authorization boilerplate on every RPC from the client.