Added support for is_ready() on device. This still need some works in some...

Added support for is_ready() on device. This still need some works in some cases for devices without attributes.. but this does the tricks right now

git-svn-id: https://redmine.imt-atlantique.fr/svn/xaal/code/Python/branches/0.7@2984 b32b6428-25c9-4566-ad07-03861ab6144f