Fix Centos Initramfs Grow Root setup

Currently the centos packer script downloads a git repo in order to manage initramfs and cloud-init-growroot.

There is a dracut module that handles this without having to install git, clone a repo, and create a seperate initramfs.

It just installs ```dracut-modules-growroot``` and then tels dracut to recreate the initramfs.

Ihave tested this packer script and it grows the root partition without any issues.
We still need to remove these files. Please keep this in.