[WIP] clod-init: Adding cloud init support

[gbenhaim]

1. user-data and meta-data can be specified directly under the cloud-init key in each
   domain definition. The content can be specified explicitly or by adding path to a file.

2. For each domain, ISO file is generated and attached to the domain.

3. Default settings can be found in the default templates which later will be modified using Jinja.

4. Merge between user defined settings and default setting is done by utils.deep_update

Example:

domains:
  atomic-el:
    cloud-init:
      user-data:
        write_files:
          - path: /root/test
            content: bla_bla_bla
        users:
          - name: galito
        chpasswd:
          list: |
            galito:galgal

Signed-off-by: gbenhaim galbh2@gmail.com

[gbenhaim]

ci test please

[gbenhaim]

I still need to complete the docstrings and do some cosmetics, but the overall functionality and basic unit/functional tests are implemented.