qa/tasks/cephfs/cephfs_test_case.py: skip cleaning the core dumps

qa/tasks/cephfs/cephfs_test_case.py: skip cleaning the core dumps

|/usr/libexec/abrt-hook-ccpp %s %c %p %u %g %t e %P %I %h

If the first character of this file is a pipe symbol (|), then the
remainder of the line is interpreted as the command-line for a
user-space program (or script) that is to be executed. More detail,
please see: http://man7.org/linux/man-pages/man5/core.5.html

Here will just skip cleaning the core dumps in this case.

Fixes: https://tracker.ceph.com/issues/45530
Signed-off-by: Xiubo Li <xiubli@redhat.com>