RootXMLParser: check_needed become a member.

This way, it can guess some parameter.

Change-Id: Id3de06195420c04fe49a330eb1d80c348172e19c
Reviewed-on: http://gerrit.aldebaran.lan:8080/11002
Reviewed-by: fmichea <fmichea@aldebaran-robotics.com>
Tested-by: gerrit
Tested-by: ncornu <ncornu@aldebaran-robotics.com>