Improve repr for MappedLUN

Give a little more info so mappedluns for nodeacls within a given TPG are
different.

Signed-off-by: Andy Grover <agrover@redhat.com>
Revert "Increase MAX_LUN to 16383"

This reverts commit 67eb46d88d3d6ccdcde4e8f7d55c959d49878a5a.

This change was premature. We need to wait to increase this until
upstream implements support for more LUNs.

Signed-off-by: Andy Grover <agrover@redhat.com>
Add support for NodeACLGroup

NodeACLGroup allows clients to pretend that LIO supports initiator groups.
It logically groups all NodeACLs with the same tag into a NodeACLGroup.

NodeACLGroup's interface is similar but not identical to NodeACL. NodeACLGroup's
interface just uses WWNs (strings) and MappedLUNGroup, so it should be possible
to use these without any use of NodeACL or MappedLUN.

Significant testing and developmental feedback from Gris Ge <fge@redhat.com>.

Signed-off-by: Andy Grover <agrover@redhat.com>
Merge pull request #56 from agrover/dev-groups

Initiator groups