Allow PostJSON to optionally receive a token, handle 401.

There is a legitimate case that will pop up in docker-machine where a
saved bearer token will expire in thirty days. We want to return a
slightly helpful message on a 401 for that case.
Allow a server to be created.

This is far from perfect, but it works.
Statuses can be fetched and checked for completion.
Basic ability to fetch a server form its self link.
Simplify SavableEntity interface with a Request object.
Use Request object in GetJSON, too.

The similarities between the two util methods and their associated test
implementors are becoming more clear.
Simplify testRequestor.
Allow adding of Public IP Addresses to Servers.
Move some JSON to fixtures_test.
Add IPAddresses to server fetch.

These are pretty different than the PublicIPAddress stuff and probably
can't/shouldn't share a struct.
Don't export CLCRequestor.
Include error messages in RequestError if available.

Depending on how much we want to hold people's hands with default vaules
and such, this might be all we need. Read the docs, use the error
messages to change your submission.
Merge pull request #7 from CenturyLinkLabs/server-creation

Server creation