qa/tasks/mgr/test_progress.py: deal with pre-exisiting pool

qa/tasks/mgr/test_progress.py: deal with pre-exisiting pool

Problem:
Currently, the test will fail we try
to remove a pool that was not created
by test_progress.py if we use the function
`remove_pool` from class CephManager
because it tracks the pools in a dictionary
and there is an assert to check if the pool
exists in the dictionary.

Solution:
Therefore, add a case where if
there is a pool that was not created
by the test, then we would delete it
through raw command instead of using
`remove_pool` from CephManager

Fixes: https://tracker.ceph.com/issues/65826
Signed-off-by: Kamoltat <ksirivad@redhat.com>