qemu-img info foo.qcow2 tries to get write lock
Description of problem:
When trying to run qemu-img info on an image which is used by QEMU qemu-img tries to acquire a write lock. Ideally this would not attempt to acquire a write lock and let qemu-img info succeed.
```
[jelle@t14s][/tmp]%qemu-img info /var/tmp/cockpit-qr_j3e_m.qcow2
qemu-img: Could not open '/var/tmp/cockpit-qr_j3e_m.qcow2': Failed to get shared "write" lock
Is another process using the image [/var/tmp/cockpit-qr_j3e_m.qcow2]?
```
Steps to reproduce:
1. Run qemu-img on an image used by a QEMU process.