Use a condition variable in LSM worker threads to sleep when there is no work to do.
Have the LSM worker track whether it found work to figure out whether to sleep or keep spinning.
Set the condition variable for LSM workers after allocating it in the manager.
Merge pull request #1195 from wiredtiger/lsm-worker-no-spin

Use a condition variable in LSM worker threads to sleep when there is no work to do