The `osd_pool_default_crush_rule` is set based on `crush_rule_variable`, which
is the output of a `grep` command.

However, two consecutive tasks can set that variable, and if the second task is
skipped, it still overwrites the `crush_rule_variable`, leading the
`osd_pool_default_crush_rule` to be set to `ceph_osd_pool_default_crush_rule`
instead of the output of the first task.

This commit ensures that the fact is set right after the `crush_rule_variable`
is assigned, before it can be overwritten.

Closes #5912

Signed-off-by: Benoît Knecht <bknecht@protonmail.ch>
(cherry picked from commit c5f7343a)