build_utils: fix collect_ceph_logs function

build_utils: fix collect_ceph_logs function

typical error from ceph-volume tests:

```
ERROR! the playbook: /home/jenkins-build/build/workspace/ceph-volume-prs-lvm-centos8-bluestore-dmcrypt/tests/functional/collect-logs.yml could not be found
```

Since `collect-logs.yml` is maintained in ceph-ansible repository,
when `collect_ceph_logs` is called from a job different from
ceph-ansible, the path is incorrect.
The idea is to make ceph-volume jobs override this path.

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>