mgr/dashboard: Fix random E2E error in mgr-modules

mgr/dashboard: Fix random E2E error in mgr-modules

This test failed at random times when it tried to find the new value of pool_ids
in the balancer module.
This happened because the value of pool_ids is automatically reverted by ceph,
so in some situations when we tried to read the new value,
it was already reverted and failed.

Enhanced the tests to be able to use any text input, not only the ones with
empty default values.

Fixes: https://tracker.ceph.com/issues/45445
Signed-off-by: Tiago Melo <tmelo@suse.com>