Increase LVM implementation robustness in order not to crash on

	Increase LVM implementation robustness in order not to crash on
	configurations like pvmove. Previously code assumed that in some places
	only lvs or only pvs are used whereas it seems that they are used
	interchangeably.

	* grub-core/disk/lvm.c (read_node): New function.
	(read_lv): Use read_node.
	(grub_lvm_scan_device): Use only first mirror on pvmove'd lvs.
	Match volumes only at the end when all lvs are found. Take both
	pvs (first) and lvs (second) into account.
	* include/grub/lvm.h (grub_lvm_segment): Merge fields stripe_* and
	mirror_* into node_*. All users updated.
	(grub_lvm_stripe): Merge this ...
	(grub_lvm_mirror): ... and this ...
	(grub_lvm_node): ... into this. All users updated.