add support for "packer.sh centos vagrant"

1.changed packer/packer.sh
2.added packer/vagrant/packer_centos.json
3.changed packer/vagrant/packer_ubuntu.json
4.added packer/vagrant/scripts/vagrant.sh for cents provisioning.
Revert "add support for "packer.sh centos vagrant""

This reverts commit 0417d92e1c929a265e47cf4168a09d61c4c70f03.
Revert "Revert "add support for "packer.sh centos vagrant"""

This reverts commit e5a4c070e656134503c385deebba5714f606a82c.
cents boot command file
Merge pull request #2 from PageLearning/master

add support for "packer.sh centos vagrant"