qa/cephfs: use run_ceph_cmd() when cmd output is not needed

qa/cephfs: use run_ceph_cmd() when cmd output is not needed

In filesystem.py and wherever instance of class Filesystem are used, use
run_ceph_cmd() instead of get_ceph_cluster_stdout() when output of Ceph
command is not required.

Signed-off-by: Rishabh Dave <ridave@redhat.com>
(cherry picked from commit 0a781ef0807ae9473fb1306ef07036226ca4f1a6)

Conflicts:
	qa/tasks/cephfs/filesystem.py
	Patches from commit coudn't be applied because lines being
	modified were present on main branch but aren't present on
	quincy branch.