The dib_env_vars variable in the Bifrost's dib.yml file can contain
the DIB_BLOCK_DEVICE_CONFIG environment variable which is always the
Multiline-YAML data. By default, the format of the data is not
preserved while the configuration is merged and saved for the
bifrost-deploy container.

This is because Ansible uses the PyYAML library which has a default
80 symbol string length limit. The official Ansible documentation [1]
recommends using to_yaml or to_nice_yaml filters with width parameter.
This change adds the same ability to the merge_yaml Ansible plugin.

1. https://docs.ansible.com/ansible/latest/user_guide/playbooks_filters.html#formatting-data-yaml-and-json



The related change for the diskimage-builder to solve the issue with
incorrect data provided by Kolla-Ansible is also provided:
I3b74ede69eb064ad813a9108ec68a228e549e8bb

Closes-Bug: #2014980
Related-Bug: #2014981
Change-Id: Id79445c0311916ac6c1beb3986e14f652ee5a63c
Signed-off-by: Maksim Malchuk <maksim.malchuk@gmail.com>