fix #1452: also log stderr of remote command with insecure storage migration

fix #1452: also log stderr of remote command with insecure storage migration

Commit 8fe00d99449b7c80e81ab3c9826625a4fcd89aa4 already
introduced the necessary logging for the secure code path,
so presumably the bug was already fixed for most people.

Delay the potential die for the send command to be able to log
the ouput+error from the receive command. Like this we also see e.g.
'volume ... already exists' instead of just 'broken pipe'.

Signed-off-by: Fabian Ebner <f.ebner@proxmox.com>