userguide: update ec2 command to reflect the precation of SOAP API

Yet another deprecation from EC2. Now the EC2 command does not support
anymore the SOAP API. On the command line it means that cerificate are
not necessary but instead we should use access keys.
commands: supports different filesytems types

improve generation of fstab so we can support different filesystems
commands: create bundle now wants different grub parameters

now grub root definition should be left as it is
no more changing hd0,0 into hd0 (since hd0 now does not work)
commands: bundle AMI finally working

After a 4 days of struggles.... So the final problem is that with
/opt/ec2/bin/ec2-bundle-image you need to pass a disk file without
the partition table, so for the moment the only solution I found is
create another file without the first kilobyte