Better ACLs handling

This merge request intents to fix and improve Rear handling of ACLs

1. Regression fix
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First, there is a commit which fix a regression introduced by 2d54454 (in 13_include_fs_code).

As I already explained, tune2fs options parsing is broken because the field separator in disklayout.conf is a space. 
Also, a comma as separator is a non sense because multiple options must be keep together (eg: default_mount_options)


2. Default mount options saving (dependent of the previous commit)
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In RHEL, the default installer behaviour on EXT* FS is to keep the acl mount option as a default mount option.

So, this commit fix that by saving them in disklayout.conf and then restoring them in the same way as the other tune2fs options.


3. Copy of users and groups
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I added a new variable (CLONE_ALL_USERS_GROUPS) to allow the end user to use all its users and groups on the rescue media. Of course, it overrides CLONE_USERS and CLONE_GROUPS if defined to y. By default it's set to n, so it's the current behaviour.
Only users not already in the Rear default passwd/group files are copied.

An option like that can be usefull in the case of ACLs defined for local users which can't be restored whithout the user defined ("cannot acl from text" error)