Small documentation update

- Recommend Vagrant 1.4
- Add step to install vagrant-aws plugin
- Add example Berkshelf install command
Use vagrant-omnibus to install Chef Solo

This is less hacky, and provides progress report during installation.
Remove nasty sudo workaround

With the release of Vagrant 1.4, we can now use a PTY with SSH to avoid
the sudo errors. There are some a couple of undesirable side-effects
though:

- Much more verbose console output.
- `./up` sometimes hangs at `* service[mongod] action restart`. Seems to
  be triggered when there are key presses when the script is running.
Minor change of comments
Print time taken for Berkshelf and Vagrant
Add option for EBS optimized EC2 instances

We can use this now that Vagrant 1.4 is released. Disabled by default as
it's more expensive and usually only useful with the even more expensive
provisioned IOPS.