Skip max fs size check on snapshot delta creation

We introduced PLOOP_MAX_FS_SIZE=16T limit after ploop was released.
To avoid snapshot creation failurem use the parent delta size as is.

Reference: PSBM-24102 "Offline resize down of ploop does not update ploop header"
Reference: ploop@957058
Reviewed-by: mpatlasov

[kir@openvz.org: fix a typo in a comment]
ploop.c: remove 'di->nimages == 0' check

This check is performed in the validate_disk_descriptor()
while parsing DiskDescriptor.xml

Reference: ploop@964766
BUGFIX Redesing the read DiskDescriptor functionality DiskDescriptor represents the images stacked configuration and should be in consistend state before the action starts. The DiskDescriptor.xml could be modified. after read and before lock.

This patch added set of functions to change read DiskDescriptor.xml logic after lock

ploop_open_dd() - allocated
ploop_lock_dd() - lock and rered
ploop_unlock_dd() - unlock
ploop_close_dd() - release

bug #PSBM-21570

Issues:
Affects Major Issue PSBM-21570 - "CLONE - Subsequent vzabackup after the interrupted one fails to merge snapshot" https://jira.sw.ru/browse/PSBM-21570

git-svn-id: https://svn.parallels.com/parallels/vzlin/utils/current/ploop@964773 3f79cd19-dd19-0410-83c5-8b167e6f9dce

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Makefile.inc: fix dpkg-architecture handling

If dpkg-architecture is not available, DEB_HOST_MULTIARCH will still be
set (to an empty value) so 'ifdef' is always true and we end up with
LIBDIR=/usr/lib/ which is not what we want.

Plus, there can be a case when dpkg-architecture binary is there
but doesn't work as it should (for example, on my Gentoo box with
dpkg ebuild installed).

To fix, let's assume that no output from dpkg-architecture means it's
either absent or failed, and we should try other means of finding out
the proper LIBDIR value.

Alternative, more complicated version is:

 DEB_HOST_MULTIARCH ?= $(shell dpkg-archistecture \
		-qDEB_HOST_MULTIARCH 2>/dev/null || echo Error)
 ifneq "$(DEB_HOST_MULTIARCH)" "Error"

But it looks more complicated and doesn't do any more good.

https://bugzilla.openvz.org/2877

Reported-by: "slepnoga ( Andrei Vinogradov )" <spamslepnoga@inbox.ru>
Signed-off-by: Kir Kolyshkin <kir@openvz.org>