Log currentOp information to mongod log

If mongod hangs it can be useful to have currentOp information to identify what ops are running. But when mongod is hung it may not be possible to connect to obtain currentOp, or if it is possible, a system administrator who is focused on restoring function may not do so.

We could log currentOp in mongod, possibly

• periodically, for example once per minute
• when clean shutdown is attempted
• when clean shutdown is attempted but gets stalled