At the end of it's execution, the metadata salvage csuite test, test/csuite/wt4156_meta_salvage, removes the core files it has created by calling rm -rf core*. This doesn't match the core_pattern on Evergreen hosts, which creates cores of the form, dump_<progname>.<pid>.core 

We should update wt4156_meta_salvage so that it also cleans up its cores on Evergreen. This will avoid the problem of an engineer seeing the core in the artifacts from a BF and assuming that it is the result of a test failure.