ceph-ansible-pr-syntax-chec: add test_ceph_release_in_ceph_default

ceph-ansible-pr-syntax-chec: add test_ceph_release_in_ceph_default
function

This new function searches for statements like '    -
ceph_release_num[ceph_release] ' in the ceph-defaults role. These must
never be used since the ceph_release is set by role running after
ceph-defaults.
However, the ceph-ansible ci passes this variable when running so it's
always defined, even before ceph-defaults runs. This is particularity
from our CI. So this is done, our Ci won't complain but general users
will end with an error like "'dict object' has no attribute" since the
variable does not exist at the time of the ceph-defaults play.

Signed-off-by: Sébastien Han <seb@redhat.com>