CurOp::completeAndLogOperation should not hang waiting for global lock

When logging a command (either slow or when forced logging is enabled) CurOp::completeAndLogOperation attempts to take a global lock to obtain storage statistics. If something else has a Global X lock (or an enqueued Global X lock), this lock acquisition will stall behind that operation. This introduces an undesirable dependency on the global lock for otherwise lock-free operations such as $currentOp.

We should give this acquisition a very short deadline and elide the storage stats when it is not available.