MAR-218: Switch to using task imports instead of includes:

- Should result in somewhat faster run, except the includes happen
during planning phase. None of the changed includes will have
problem with this.
- Solves the issue of (included) imported tasks not being tagged
properly, particularly in relation to the mechanism for explicitly
running all handlers.

MAR-218: Switch to using fully-qualified collection names for all tasks:

- Ensures there is no ambiguity when invoking a module.

MAR-218: Quote all octal values in YAML files:

- Fixes linting errors, and ensures there is no ambiguity in case of
YAML specification changes.

MAR-218: Fix include invocations:

- The old include keyword/task has been deprecated in favour of more
explicit include_tasks one.

MAR-148: Fixing linting errors:

- Do not compare against booleans when value is already boolean in
"when" conditions.
- Use pipefail in conjunction with setting the shell to Bash when
extracting the backup encryption key IDs.
- Do not compare variables to empty strings in "when" conditions. This
change currently works only for complex variables (stuff can break
badly in case of simple variables in current default Ansible
configuration).
- Fix missing space in one of Jinja2 templates.

MAR-135: Switch to using run_handlers instead of handlers as variable:

- Updated all roles to now depend on run_handlers being set to True in
order to force execution of handlers.

MAR-114: Updated task syntax for backup roles:

- Updated backup, backup_client, and backup_server.
- Added and removed quoting where it makes sense.
- Switched to using expanded syntax (instead of one-liners).
- Updated ordering of arguments in task definitions.

MAR-109: Minor fixes to backup role:

- Fixed mode parameters used in the role to include leading zero.