Fix issue where exclusive allocations wouldn't lay tasks out correctly

with CR_PACK_NODES.

Really do commit d388dd67 a different way to get the same info and
be able to lay out tasks correctly when --hint=nomultithread.

tests on a 4 core 8 thread system are
srun -n6 --hint=nomultithread --exclusive whereami | sort -h
srun: cpu count 6
   0 snowflake0 - MASK:0x1
   1 snowflake0 - MASK:0x2
   2 snowflake0 - MASK:0x4
   3 snowflake0 - MASK:0x8
   4 snowflake1 - MASK:0x1
   5 snowflake1 - MASK:0x2

and

srun -n10 -N5 --hint=nomultithread --exclusive whereami | sort -h
srun: cpu count 10
   0 snowflake0 - MASK:0x1
   1 snowflake0 - MASK:0x2
   2 snowflake0 - MASK:0x4
   3 snowflake0 - MASK:0x8
   4 snowflake1 - MASK:0x1
   5 snowflake1 - MASK:0x2
   6 snowflake1 - MASK:0x4
   7 snowflake2 - MASK:0x1
   8 snowflake3 - MASK:0x1
   9 snowflake4 - MASK:0x1