Run httpd-admin and smwingsd in "adm" group. Refs #2492

httpd-admin is run as srvmgr system user, which is member of the "adm"
group.

Any user in "adm" group will be granted unlimited access to "db",
"config" and other administrative commands.
*.spec.in: cleanup %preun script. Refs #2536
Restore httpd-admin symlink to httpd executable. Refs #2536
httpd-admin log files moved to /var/log/httpd-admin/. Refs #2551

Added also configuration file for logrotate.
Moved /etc/sudoers template fragment to nethserver-base. Refs #2492
Fix permissions on *-update event. Refs #2492

Cleanup and fix permissions on files under
/var/cache/nethserver-httpd-admin/ directory.