Move LSM configuration options to be a group in WT_SESSION->create API.

This pull request isn't ready to be merged yet, but I wanted to see the results of testing.

We need to update some Jenkins jobs in co-ordination with merging this pull request. The particular jobs are: perf-med-lsm, perf-med-lsm-sleep, perf-update-lsm.

This pull request addresses issue #379