Flag day for AI manifest missing slice size

RE: bug 7794 - http://defect.opensolaris.org/bz/show_bug.cgi?id=7794

With the fix of this bug, installadm(1m) of the OpenSolaris Automated Installer no longer requires tag slice_size in the slice_action="delete" or slice_action="preserve".  So, for these cases, slice_size is no longer needed, but will be tolerated so as not to force users to change manifests immediately.  It is suggested that slice_size be removed for delete and preserve since it may be confusing to users later.  It is also possible that more stringent future validation might regard the tag as an error in these cases.

The corresponding change has been made for fdisk partitions - partition_type, partition_size are not necessary for the delete action

The change in the RNG schema for the AI manifest, more thoroughly explained in the bug comments, separates handling of actions for both slices and fdisk partitions so that the manifests can be individually screened for required tags per different action:

- for slice create, number and size are required
- for slice delete and preserve, number is required
- for partition delete, either partition number or starting sector is required (along with optional partition size)
- for partition create, size is required

If the above required tags are missing for the action, the manifest will not pass validation in "installadm add".  If these tags were missing before, the manifest would pass validation, but the installation would fail, so the only change here is that the user is informed of the problem during manifest validation on the server.

List of formerly required tags that may now be removed:
- slice_size for slice_action=delete, preserve
- partition_type where partition_action=delete
- partition_number for partition_action=create, or partition_action=delete where deletion is to be done by partition_offset with optional partition_size
- partition_start_sector, partition_size for partition action=delete when deleting by partition_number

So once again:
- changes are not necessary at this time
- missing required tags for particular operations will cause the manifest to fail AI server-side validation henceforth
- suggest removing slice_size, partition_size, partition_number in contexts where they are not required