A large refactor of packer templates

- .gitignore added to remove packer_cache from index
- Documentation has been added with detailed explanation how to build
  the image, what was changed
- A structure change:
  * A new structure has one directory for ubuntu, debian. This allows to
    remove code duplication in bash scripts. Later, template for centos
    can be easily incorporated.
  * script directry contains post-processor scripts for all
    distributives
  * scripts/debian directory contains only changes specifig to Debian
    family (Debian, Ubuntu)
- packer templates
  * Code has been separated from variables.
  * virtualbox builder has been added

Change-Id: If96d86cead153019dddcffe2256b2d5ab9b41adf
Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>

doc/PACKER.md

@@ -0,0 +1,67 @@
+# [Packer](https://www.packer.io) Templates
+
+The most of settings are specified as variables. This allows to override them
+with `-var` key without template modification. A few environment variables
+should be specified as a safety measure. See `debian.json` `ubuntu.json` with
+the post-processors section with all details about deploying the Vagrant Boxes
+to Atlas.
+
+## Custom builds
+
+### Ubuntu build
+
+```sh
+  UBUNTU_MAJOR_VERSION=16.04 \
+  UBUNTU_MINOR_VERSION=.1 \
+  UBUNTU_TYPE=server \
+  ARCH=amd64 \
+  HEADLESS=true \
+  packer build -var 'cpus=2' ubuntu.json
+```
+
+### Debian build
+```sh
+  DEBIAN_MAJOR_VERSION=8 \
+  DEBIAN_MINOR_VERSION=5 \
+  ARCH=amd64 \
+  HEADLESS=true \
+  packer build -var 'cpus=2' debian.json
+```
+
+## Login Credentials
+
+(root password is "vagrant" or is not set )
+
+* Username: vagrant
+* Password: vagrant
+
+SSH_USER may be used to create a different user whci may be used later to
+access environment.
+
+## VM Specifications
+
+* Vagrant Libvirt Provider
+* Vagrant Virtualbox Provider
+
+### qemu
+
+* VirtIO dynamic Hard Disk (up to 10 GiB)
+
+#### Customized installation
+
+Debian configuration is based on 
+[jessie preseed](https://www.debian.org/releases/jessie/example-preseed.txt).
+Ubuntu configuration is based on 
+[xenial preseed](https://help.ubuntu.com/lts/installation-guide/example-preseed.txt).
+A few modifications have been made. Use `diff` for more details.
+
+##### Debian/Ubuntu installation
+
+* en_US.UTF-8
+* keymap for standard US keyboard
+* UTC timezone
+* NTP enabled (default configuration)
+* full-upgrade
+* unattended-upgrades
+* /dev/vda1 mounted on / using ext4 filesystem (all files in one partition)
+* no swap