nuageinit: readd ssh key parsing when key is in meta_data.json
    
    in openstack when no user is specified but a sshkey is provided
    the information is stored in meta_data.json under "public_keys"
    
    PR:	280461
    Reported by:	tdb
    
    (cherry picked from commit 19fb9ad746517c7af9d79a982334b2550f285355)