Add --xattrs to Overcloud backup

We are missing to add --xattrs when running the
Overcloud backup.

Change-Id: I8250f8e9882c25bb6a0333d36d3928b2c5219b0a

doc/source/install/controlplane_backup_restore/02_overcloud_backup.rst

@@ -109,7 +109,7 @@ paths to backup is as much general as possible.
 The following folders should be backed up::
 
   mkdir -p /var/tmp/filesystem_backup/
-  tar --ignore-failed-read \
+  tar --xattrs --ignore-failed-read \
       -zcvf /var/tmp/filesystem_backup/fs_backup-`date '+%Y-%m-%d-%H-%M-%S'`.tar.gz \
       /etc/nova \
       /var/log/nova \

doc/source/install/controlplane_backup_restore/04_overcloud_restore.rst

@@ -131,7 +131,7 @@ directory and uncompress all the data::
   mkdir /var/tmp/filesystem_backup/data/
   cd /var/tmp/filesystem_backup/data/
   mv <path_to_the_backup_file> .
-  tar -xvzf <backup_faile>.tar.gz
+  tar --xattrs -xvzf <backup_file>.tar.gz
 
 NOTE: Untarring directly on the / directory will
 override your current files. Its recommended to