Add another kmem test to check for lock contention in the slab

Add another kmem test to check for lock contention in the slab
allocator.  I have serious contention issues here and I needed
a way to easily measure how much the following batch of changes
will improve things.  Currently things are quite bad when the
allocator is highly contended, and interestingly it seems to
get worse in a non-linear fashion... I'm not sure why yet.
I'll figure it out tomorrow.

        kmem:kmem_lock    Pass

   kmem_lock: time (sec)        slabs           objs
   kmem_lock:                   tot/max/calc    tot/max/calc
   kmem_lock:  0.061000000      75/60/64        2400/1894/2048
   kmem_lock:  0.157000000      134/125/128     4288/3974/4096
   kmem_lock:  0.471000000      263/249/256     8416/7962/8192
   kmem_lock:  2.526000000      518/499/512     16576/15957/16384
   kmem_lock: 14.393000000      990/978/1024    31680/31270/32768

git-svn-id: https://outreach.scidac.gov/svn/spl/trunk@134 7e1ea52c-4ff2-0310-8f11-9dd32ca42a1c