infra: use dedicated variables for balancer status

infra: use dedicated variables for balancer status

The balancer status is registered during the cephadm-adopt, rolling_update
and swith2container playbooks. But it is also used in the ceph-handler role
which is included in those playbooks too.
Even if the ceph-handler tasks are skipped for rolling_update and
switch2container, the balancer_status variable is erased with the skip task
result.

play1:
  register: balancer_status
play2:
  register: balancer_status <-- skipped
play3:
  when: (balancer_status.stdout | from_json)['active'] | bool

This leads to issue like:

The conditional check '(balancer_status.stdout | from_json)['active'] | bool'
failed. The error was: Unexpected templating type error occurred on
({% if (balancer_status.stdout | from_json)['active'] | bool %} True
{% else %} False {% endif %}): expected string or buffer.

Closes: https://bugzilla.redhat.com/show_bug.cgi?id=1982054
Signed-off-by: Dimitri Savineau <dsavinea@redhat.com>