MAR-163: Attach noqa directives to task names (if skipping is applicable on task level) for better uniformity:

- This way the indentation of comment describing the directive can
always be on the same level everywhere (irrespective of how the rest
of task arguments are listed).

MAR-163: Reformat skip-QA directives for ANSIBLE0012 (Commands should not change things if nothing needs doing):

- Update codes used to identify the disabled QA checks.
- Switch to using new syntax that disables only a specific QA check
instead of all of them on a single task.
- Drop disabling QA checks on two command tasks, since they actually
use the "creates" directive (therefore passing the QA check).

MAR-152: Drop a couple of references to Debian 8 Jessie from multiple roles:

- Mark workaround as TODO entry (so maybe it can get fixed at some
point.
- Drop SSH known hosts entries in tests for backup_server role.
- Fix some erroneous comments in tests for mail_server
role (references to Debian 8 Jessie).
- Drop reference to Debian 8 Jessie from the preseed file template.

MAR-152: Drop support for Debian 8 Jessie from the backup_client role:

- Simplify the invocation of GnuPG commands (since we don't have to
massage output formats depending on distribution version anymore).

MAR-148: Refactor handling of GnuPG backup client keyring:

- Don't use the include_tasks, it seems to cause more issues than it
helps (with linting etc).
- Directly reference all the relevant handlers as part of notification
instead.

MAR-148: Fix Ansible warnings for the backup_client role:

- Use length filter to check if optional parameter lists have been
supplied.
- Quote the crontab trigger times to avoid implicit conversion from
integer to string.

MAR-148: Use dynamic include_tasks for cleaning up the GnuPG keyring used for backup encryption and signing:

- Required due to change in Ansible - the import_tasks cannot be
notified any longer by the tasks.

Noticket: Fix the invocation of GnuPG to use the --no-tty option:

- At least in some cases GnuPG would otherwise fail to run.

MAR-132: Fix the handler that recreates the GnuPG keyring for duplicity:

- In Debian Stretch it can happen that a file (the GnuPG Unix socket)
dissappears in middle of removing the directory, causing
failures. Switch to using the "rm" command instead.

MAR-125: Eliminated a couple of warnings:

- Use the file module when cleaning-up the /etc/duply/main/gnupg directory.
- Mark the bind_password in m_ldap_entry and m_ldap_permissions as no_log
parameters.

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-108: Applied linting fixes for backup_client role:

- Ignore the two handlers for Ansible lint checks since they are only called via
notify and if user explicitly requested so.
- Simplify the playbook by installing python-pexpect unconditionally on all
versions of Debian.
- Fixed a number of file mode parameters to use leading zero.