Use correct directory when reporting core files

When core files are found, "ls" of them uses the wrong directory.
For example, in

https://jenkins01.trafodion.org/job/core-regress-seabase-cdh4.4/75/console :

 WARNING: Core files found in /home/jenkins/.../trafodion/core :
 ls: cannot access sqf/.../core.slave09.17754.sqlci: No such file or directory

The correction is to pushd to the shown directory, do "ls", and popd.

Change-Id: I8c9bc5c853418b931dd3dc359e799c6ef684cc45