fix #4390: rbd: snapshot delete: avoid early return to fix handling TPM drive

The only caller where $running can even be truthy is QemuServer.pm's
qemu_volume_snapshot_delete(). But there, a check if snapshots should
be done with QEMU is already made and the storage function is only
called if snapshots should not be done with QEMU (like for TPM drives
which are not attached directly). So rely on the caller and do not
return early to fix removing snapshots in such cases.

Even if a stray call ends up here (can happen already by changing the
krbd setting while a VM is running to flip the above-mentioned check
and the early return check removed by this patch), it might not even
be problematic. At least a quick test worked fine:
1. take snapshot via a monitor command in QEMU
2. remove snapshot via the storage layer
3. create a new file in the VM
4. take a snapshot with the same name via monitor command in QEMU
5. roll back to the snapshot
6. check that the file in the VM is as expected
Using the storage layer to take the snapshots and QEMU to remove the
snapshot also worked doing the same test. Even if it were problematic,
the check in qemu-server should rather be improved then.

(Trying to issue a snapshot mon command for a krbd-mapped image fails
with an error on the other hand, but that is also not too bad and not
relevant to the storage code. Again, it rather would be necessary to
improve the check in qemu-server).

The fact that the pve-container code didn't even pass $running is the
reason removing snapshots worked for containers on a storage with krbd
disabled (the pve-container code calls map_volume() explicitly, so
containers can work regardless of the krbd setting in the storage
configuration; see commit 841fba6 ("call map_volume before using
volumes.") in pve-container).

For volume_snapshot(), the early return with $running was already
removed (or rather the relevant logic moved to QemuServer.pm) in 2015
by commit f5640e7 ("remove running from Storage and check it in
QemuServer"), even before krbd support was added in RBDPlugin.pm.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>
Reviewed-by: Fabian Grünbichler <f.gruenbichler@proxmox.com>

PVE/Storage/RBDPlugin.pm

@@ -767,8 +767,6 @@ sub volume_snapshot_rollback {
 sub volume_snapshot_delete {
     my ($class, $scfg, $storeid, $volname, $snap, $running) = @_;
 
-    return 1 if $running && !$scfg->{krbd}; # FIXME: ????
-
     $class->deactivate_volume($storeid, $scfg, $volname, $snap, {});
 
     my ($vtype, $name, $vmid) = $class->parse_volname($volname);