Enhancements in virtualbox scripts

For better flexibility of virtualbox scripts I sugest :
1. split prepare-environment.sh into 3 actions:
- prepare-environment.sh - verifies tools availability
- clean-previous-installation.sh - deletes previous installation of Mirantis OpenStack
- create-interfaces.sh - creates host-only network interfaces
and run all actions from launch.sh consequentially.
This will allow user to skip some parts easily.
2. For thouse users who run scripts under Cygwin add into launch.sh next lines:
- read virtualbox path from registry
- add virtualbox path to PATH
3. make create_vm() function able to create VMs with OS type different than RedHat_64