Improved test script

- Added Vagrant plugin auto-install
- Fixed "VBoxManage" detection
- Stop the tests if vagrant didn't start

Note: these changes were mostly because I'm trying to run the tests on openSUSE 13.1 x84_64 and some things didn't match.

I'm still having trouble with Vagrant 1.4.3, I get this with the updated script from this PR:
```
IP for stable_on_apache_with_mysql: 192.168.10.10
Bringing machine 'stable_on_apache_with_mysql' up with 'virtualbox' provider...
There are errors in the configuration of this machine. Please fix
the following errors and try again:                                                                                                                                         

Vagrant:                                                                                                                                                                    
* Unknown configuration section 'berkshelf'.                                                                                                                                
* Unknown configuration section 'omnibus'. 
```

@Gomez any idea ? A quick Google didn't help.
Also: I'm very new to Vagrant...