block/vhdx: Make vhdx_create() always set errp

This patch makes vhdx_create() always set errp in case of an error. It
also adds errp parameters to vhdx_create_bat() and
vhdx_create_new_region_table() so we can pass on the error object
generated by blk_truncate() as of a future commit.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 20170328205129.15138-2-mreitz@redhat.com
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Max Reitz <mreitz@redhat.com>
(cherry picked from commit 55b9392b)
* prereq for 698bdfa0
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>