tests: CEPH_CLI_TEST_DUP_COMMAND=1 for qa/workunits/cephtool/test.sh

tests: CEPH_CLI_TEST_DUP_COMMAND=1 for qa/workunits/cephtool/test.sh

Run cephtool-test-{mon,osd,mds}.sh with CEPH_CLI_TEST_DUP_COMMAND=1 to
detect idempotency related problems during make check. This is how
ceph-qa-suite/tasks/workunit.py will run
suites/rados/singleton/all/cephtool.yaml and it's easier to fix when
make check fails rather than later on when a fully populated rados suite
has one failed job.

http://tracker.ceph.com/issues/11618 Refs: #11618

Signed-off-by: Loic Dachary <ldachary@redhat.com>