Description of problem:

Cloned from https://tracker.ceph.com/issues/38548

When requesting ceph-volume to print json output, messages and errors are printed to stdout.
The printed json can't be consumed given that it's seen as invalid json.

seen on ceph version 14.2.2-298-g0bdfdc6 (0bdfdc6b5433736bd11c321ecfa559f3b30f9187) nautilus (stable)

How reproducible:
100%

Steps to Reproduce:
1. ask ceph-volume to output using --format json


Actual results:
ceph-volume outputs json with extra messages in addition on stdout, which makes the json as invalid.

Expected results:
ceph-volume outputs only json data on stdout.


Typical output:

[root@osd1 /]# ceph-volume simple scan /dev/sda1 --stdout 2>/dev/null
Running command: /usr/sbin/cryptsetup status /dev/sda1
Running command: /bin/mount -v /dev/sda1 /tmp/tmp_NrdoM
stdout: mount: /dev/sda1 mounted on /tmp/tmp_NrdoM.
Running command: /bin/umount -v /tmp/tmp_NrdoM
{
"active": "ok", 
"ceph_fsid": "f3ea8c89-3b32-4abd-8aa9-07d1e6319e3b", 
"cluster_name": "ceph", 
"data": {
"path": "/dev/sda1", 
"uuid": "de0465d1-b00b-4bd6-b1da-92e8f6cf0aef" 
}, 
"fsid": "de0465d1-b00b-4bd6-b1da-92e8f6cf0aef", 
"journal": {
"path": "/dev/sdc1", 
"uuid": "b8e4707c-c28a-45fb-913f-6680a5f3b2d4" 
}, 
"journal_uuid": "b8e4707c-c28a-45fb-913f-6680a5f3b2d4", 
"keyring": "AQDSiUld6XdXGxAAksb27KOAv5/byZ9ybu8J9w==", 
"magic": "ceph osd volume v026", 
"none": "", 
"ready": "ready", 
"require_osd_release": 14, 
"type": "filestore", 
"whoami": 10
}
[root@osd1 /]#