vmapp: add the new framework to build vmapps.

> the reorganizing generating image process part of #141.

This release provides following vmapp(image.ini files):

* required:
  * load_balancer
  * centos6
  * cssandra
* demo:
  * lbnode (for load_balancer)
* optional/tests:
  * vanilla
  * selenium2-box (bonus)

if you want to try to build vmapps, you can run following commands.
```
$ cd vmapp

$ sudo ./build.sh load_balancer
$ sudo ./build.sh centos6
$ sudo ./build.sh cassandra
```