ceph-volume: Using --readonly for {vg|pv|lv}s commands

ceph-volume: Using --readonly for {vg|pv|lv}s commands

The actual code is detecting {vg|pv|lv}s by running the usual {vg|pv|lv}s commands.
Those calls expect lvmetad to be aware of the actual state of them.
This works actually pretty well in most of the cases.

When ceph-volume is run from a container,
this code also works from the container itself but don't on the host.

On the host side, running {vg|pv|lv}s commands reports nothing,
making ceph-volume reporting "No valid Ceph devices found"
The root cause is lvmetad not receiving the udev notification and so,
{vg|pv|lv}s commands reports the 'known' state instead of the 'real' state.

This is a major issue as it means that it exists cases or maybe races where
ceph-volume reports "No valid Ceph devices found" while the disk
actually have some Ceph data & metadata on them.
This could be interpreted like disks are free/available while they are not.
This will mislead users or configuration tools trying to understand the
current state of a node.

In July 2015, as per https://www.redhat.com/archives/lvm-devel/2015-July/msg00086.html,
a new option called "--readonly" have been added to lvm2.
One of the most interesting part of it is : "disable using lvmetad so VGs are read from disk"

In our case, that feature is really interesting as it means that
everytime ceph-volume calls a {vg|pv|lv}s command, it will read the
metadata from the disks instead of considering the lvmetad status.

This patch change all the {vg|pv|lv}s call to use --readonly.
It solves the bug exposed here and doesn't affect the traditional use-case.
The main benefit of this patch is to avoid a false report of a disk not having metadata.

(cherry picked from commit 7be00cd19297ec80b4a629e2fc1e79c64205402c)
Fixes: https://tracker.ceph.com/issues/23693
Signed-off-by: Erwan Velu <erwan@redhat.com>