9891 libbe slow building snapshot list

Before on a system with many snapshots, time beadm list -s
real 48.6      user 4.7      sys 43.8

real 44.6      user 4.5      sys 40.1

real 45.5      user 4.4      sys 41.0

real 44.4      user 4.5      sys 39.8
After, user time is consistently less.
real 42.6      user 2.9      sys 39.7

real 41.4      user 3.0      sys 38.3

real 40.6      user 3.1      sys 37.4

real 41.5      user 2.8      sys 38.5