Minimize WT-5043 diagnostic tests to exclude time other than eviction itself

Summary:
Minimize test diagnostics added to track WT-5043 in the hopes it will reduce false positives.

After merging WT-5120, we hit another failure of operation tracking for WT-5043: eviction-server took longer than 5 minutes on zseries.

The Jenkins job (and there is a tarball on the zseries machine) that failed is:
http://build.wiredtiger.com:8080/job/wiredtiger-test-format-stress-zseries/50139