qa: don't override with args when it's empty

qa: don't override with args when it's empty

In methods raw_cluster_cmd_result() of CephManager and LocalCephManager
and raw_cluster_cmd of LocalCephManager when keyword arguments are
passed instead of positional arguments, the methods run ceph command
with no arguments. This is because the methods do
"kwargs['args'] = args" unconditionally.

Fixes: https://tracker.ceph.com/issues/49486
Signed-off-by: Rishabh Dave <ridave@redhat.com>