Vmware docs

Per [our discussion](https://github.com/mitchellh/packer/pull/419#issuecomment-24477876), I've modified vmware.html.markdown to show a functional vmware builder config at the top and modified the example boot_command at the bottom.

I've created a 'example_configs/vwmare' dir at the top level containing
* ubuntu-12.04.2-server-config.json: mirrors the content of vmware.html.markdown
* ubuntu-12.04.2-server-preseed.cfg: a working preseed file.

Unfortunately, I can't get ubuntu to pull the preseed file from a github repo, only from gists.  If the preseed file location changes, both website/source/docs/builders/vmware.html.markdown and example_configs/vmware/ubuntu-12.04.2-server-config.json should be modified.