Use a set of {Session, Cursor} pairs ("passes") for calls into WiredTiger
to avoid a) opening a large number of Sessions or Cursors and b) avoid
reusing a Session/Cursor pair in more than one thread.  Each operation,
except folds, use the Session/Cursor pair corresponding to the scheduler
id (roughly "core") they are running on.  Each vnode instance will have
(count(schedulers) + count(active folds)) Session/Cursor pairs in use so
be sure to set session_max large enough when opening the connection to
WiredTiger.  This method will cause problems with scheduler threads going
to "sleep" so be sure to run schedmon to wake them up.