chimera: use ArrayList instead of LinedList

NFS listing is heavy with List#get operations, which
is the weakest point for LinkedList. This change improves
listing of jumbo directories ( ~100k files ) by factor of 10.

RELEASE NOTES:
speedup directory listing of large directories

Acked-by:
Target: master, 2.6
Require-book: no
Require-notes: yes