Tutorial environment upgrade notes -  699

Here are a couple of options for upgrading the tutorial environment. 
 1. Destroy and recreate
 2. yum upgrade to the desired flocker-node version

I wasn't sure whether to include the second option, but it might be interesting to people who are familiar with yum and RPMs. Also might be better for those people who have gone beyond the tutorials and created their own application configurations within our tutorial environment. Perhaps I ought to add those reasons to the document.

The yum upgrade option works because #510 has now been resolved. So in fact the `yum install` lines can be simplified, which I'll do in a separate pull request (#702).

Fixes #699
`|version|` works in the paragraph below but not in the code-block. @tomprince do you have any ideas to get round this?

We could just keep the example number the same, and have the sentence say "Only proceed if you find that you are running an older version of Flocker than |version|".

When I use `|version|` now I get 0.1.2-75-g5d8fdc3. I'm assuming that this will be fine in released docs and anyone using "latest" docs can figure it out.