Expose ec2test package

[ngauthier]

Hello! I'm just getting started with goamz, and I wanted to write tests around my wrapper for the goamz client. The idea would be something like this:

1. Set up a fake ec2 endpoint
2. Initialize a goamz ec2 client pointed to the fake endpoint
3. Initialize my wrapper client with the goamz client
4. Call a method on my wrapper client
5. Inspect my fake endpoint to see that the appropriate API call was made.

I stumbled upon the ec2test package and it looks like it's used internally by the ec2 package to test the api. I was wondering if we could expose some of the fields and methods publicly, for example Server.reqs, so that I could access the actions made in my tests.

I would be happy to make and contribute this change to goamz. I'm just looking for a :+1: and any guidance from the maintainers of the project to make sure I don't do anything you wouldn't like me to.

-Nick