create_efidisk: poll the real size after volume creation

create_efidisk: poll the real size after volume creation

some storage backends have bigger granularity than the default 128k
size from the EFIVARS template file, so we actually need to poll the
real created disk size, as it will be used to create the target
volume for local storage migration on running VMs, if it's to small
the target will be to small and migration will fail.

Just a fix for newly created EFIDISKS, for others we need to rescan
the size after we've got the migrate lock and write the updated info
out, so that the target node has the correct one (protected from
migrate lock).

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>