ceph-perf-pull-requests: add ceph-perf-classic job

ceph-perf-pull-requests: add ceph-perf-classic job

* add "ceph-perf-classic" job. this job is defined using the job
  template of "ceph-perf-{osd_flavor}"
* change the whitelist of "ceph-perf-crimson" and "ceph-perf-classic"
  to "performance", so both of them can be enabled as long as the
  "performance" label is attached to a PR.

please note, "ceph-perf-classic" job is using the test case and
acceptance critiera defined in `src/test/crimson/cbt/radosbench_4K_read.yaml`
for testing the performance. we need to adapt it for the needs of
classic OSD.

Signed-off-by: Kefu Chai <kchai@redhat.com>