ceph-volume: remove stderr in has_bluestore_label()

We don't want to generate this log when a call to
`has_bluestore_label()` fails.

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

src/ceph-volume/ceph_volume/util/device.py

@@ -321,7 +321,7 @@ def is_ceph_disk_member(self):
     def has_bluestore_label(self):
         out, err, ret = process.call([
             'ceph-bluestore-tool', 'show-label',
-            '--dev', self.abspath])
+            '--dev', self.abspath], verbose_on_failure=False)
         if ret:
             return False
         return True