Currently some roles may be somewhat unreliable in different ways. These roles should really be improved to be more robust so there wouldn't be any surprises during failures, reruns, etc.

The following should be fixed in different roles:
* '''backup_client'''
** Extraction of key identifiers should also include checks for content. I.e. bail-out in case the mandatory key IDs are not successfully extracted.
* '''mail_forwarder'''
** Purging of Exim configuration should be moved from a handler to task, since it is idempotent.
*'''preseed'''
** '''ansible_key''' documentation is incorrect - this should be value, not path to ssh key.
*'''common'''
** '''ca_certificates''' should be a dictionary describing deployed certificate files. Keys should be filenames, values should be certificates themselves (currently it's a list of file paths).
* '''ldap_server'''
** '''ldap_server_tls_certificate''' should be certificate content itself instead of a file path.
** '''ldap_server_tls_key''' should be key content itself instead of a file path.
* '''xmpp_server'''
** '''xmpp_tls_certificate''' should be certificate content itself instead of a file path.
** '''xmpp_tls_key''' should be key content itself instead of a file path.
* '''mail_server'''
** '''imap_tls_certificate''' should be content instead of a file path.
** '''imap_tls_key''' should be content instead of a file path.
** '''smtp_tls_certificate''' should be content instead of a file path.
** '''smtp_tls_key''' should be content instead of a file path.
* '''web_server'''
** '''default_https_tls_key''' should be content instead of a file path.
** '''default_https_tls_certificate''' should be content instead of a file path.
* '''php_website'''
** '''https_tls_key''' should be content instead of a file path.
** '''https_tls_certificate''' should be content instead of a file path.
* '''wsgi_website'''
** '''https_tls_key''' should be content instead of a file path.
** '''https_tls_certificate''' should be content instead of a file path.
* '''all roles'''
** Introduce optional execution of all handlers in tasks via custom variable and include directive. The purpose is to allow for execution of handlers only in case of some failed run, since certain handlers are used to bring the system to consistent state. Unfortunately, tagging can't be used for this purpose, and custom variable is needed instead. The handlers should not be auto-executed during regular runs.