With -blockdev we must look up via the nodename rather than the 'drive'
alias which is not present any more.

This fixes the pre-creation of storage volumes on migration with
non-shared storage.

https://bugzilla.redhat.com/show_bug.cgi?id=1793263Signed-off-by: NPeter Krempa <pkrempa@redhat.com>
Reviewed-by: NMichal Privoznik <mprivozn@redhat.com>