tests: ceph create may consume more than one id

tests: ceph create may consume more than one id

When CEPH_CLI_TEST_DUP_COMMAND=1 is set, ceph osd create will consume
two osd id and return the later. Fix the test to account for that and
not assume the osd id being allocated by osd create is always the
next available osd id.

The other osd create tests do not suffer from the same variation because
they provide a UUID argument that guarantees the same osd id is going to
be returned every time.

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

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