lvm: suppress logs on stdout when expecting json output

Apparently lvm sometimes logs messages to stdout (instead of stderr),
which messes up json format. Disable those messages by passing --quiet
option.

Fixes QubesOS/qubes-issues#10023

Author: marmarek

qubes/storage/lvm.py

@@ -234,6 +234,7 @@ def usage_details(self):
 _init_cache_cmd = [
     _lvm,
     "lvs",
+    "--quiet",
     "--noheadings",
     "-o",
     "vg_name,pool_lv,name,lv_size,data_percent,lv_attr,origin,lv_metadata_size,"