includedir in suoders can be prefixed by "arroba"

Since version 1.9.1, @includedir can be used in the sudoers files
instead of #includedir:

https://github.com/sudo-project/sudo/releases/tag/SUDO_1_9_1

This happens to be the default in SUSE Linux enterprise sudoer package,
so cloudinit should take this into account.

Otherwise, cloudinit was adding an extra #includedir, which was
resulting on the files under /etc/sudoers.d being included twice, one by
@includedir from the SUSE package, one by the @includedir from
cloudinit. The consequence of this, was that if you were defining an
Cmnd_Alias inside any of those files, this was being defined twice and
creating an error when using sudo.

Signed-off-by: Jordi Massaguer Pla <jmassaguerpla@suse.de>

cloudinit/distros/__init__.py

@@ -673,7 +673,7 @@ def ensure_sudo_dir(self, path, sudo_base='/etc/sudoers'):
         found_include = False
         for line in sudoers_contents.splitlines():
             line = line.strip()
-            include_match = re.search(r"^#includedir\s+(.*)$", line)
+            include_match = re.search(r"^[#|@]includedir\s+(.*)$", line)
             if not include_match:
                 continue
             included_dir = include_match.group(1).strip()