Convert `%NAME%` to `{{ .Name }}` to prevent blocking error on VM boot

My `boot_command` had this in it: `hostname=%NAME%`

That resulted in a blocking error when configuring the network.

> The name "%NAME%" is invalid.

![screen shot 2013-06-29 at 12 42 02 am](https://f.cloud.github.com/assets/353790/725525/48e8f3ae-e076-11e2-8bbd-05bb47def246.png)

d80e230 just adds substitution for `%NAME%` => `{{ .Name }}`, which resolves the issue for me.