Improve error handling in Pooler and Auth classes

[briancain]

• Add more errors to error class to be raised
• Update Auth class to raise errors instead of just returning nil if something goes wrong
• Update Pooler class to raise more errors when responses are not ok
• Handle raised errors in command class

[briancain]

@johnmccabe sorry to make some additional changes on you...but I'm planning on making the Pooler and Auth class raise error specific messages when things go wrong instead of just returning nil. This should hopefully make things a lot easier to handle as a consumer when something goes wrong.

[briancain]

An example of what that's going to look like will be here: 05e9d5a

And then consumers of those classes can use the rescue methods in ruby for all the various vmfloaty/errors that I'll add.

[johnmccabe]

Sounds good, I'll add handling later this evening.

[briancain]

@johnmccabe - I'll let you know when the gem is released, probably later today :)