SERVER-13635: make some tests more generic for some engines
SERVER-14425 Cleanup LockerImpl

* Remove unused methods
* Make references to the lock manager to go directly through the instance
* Add comments
SERVER-14425 Performance optimization in LockManager for the unlock path
SERVER-14425 Make MMAP V1 code in LockerImpl conditionally compiled

This change cuts down on the locking work that other storage engines have
to do.
SERVER-13635: do not invalidate doc when using doc locking
SERVER-13635: make sharding test more robust
SERVER-14425 Add MMAP V1 check to invariant
Merge remote-tracking branch 'upstream/master'