Add an operation field to know where threads hang

There has been another failure of the child process in schema_abort. The changes from WT-4248 was not adequate. Basically, all the threads doing schema operations hang and do not advance the timestamp so the program aborts after 10 seconds of waiting for them to make forward progress.

We do not have a core dump from this to know what operations those threads were hung in because it is a sanitizer run.
http://build.wiredtiger.com:8080/job/wiredtiger-clang-sanitizer/3348/console

We can hope this dies on a job that is not sanitizer so that we get a core dump.