ceph_volume: fix bug in `is_lv()`

This function makes the `ceph_volume` module be not idempotent in
containerized context because it tries to run a container and bindmount
directories that no longer exist.

In that case, the `lvs` command being executed returns something
different than `0` so we can't call `json.loads(out)['report'][0]['lv']`
since it might throw an python error.

The idea is to return `True` only if `rc` is equal to `0` and
`len(result)` is greater than `0`, which means the command matched an
LV.

Fixes: #6284

Signed-off-by: Guillaume Abrioux <gabrioux@redhat.com>

library/ceph_volume.py

@@ -446,10 +446,11 @@ def is_lv(module, vg, lv, container_image):
 
     rc, cmd, out, err = exec_command(module, cmd)
 
+    if rc == 0:
         result = json.loads(out)['report'][0]['lv']
-    if rc == 0 and len(result) > 0:
+        if len(result) > 0:
             return True
-    else:
+
     return False