In case of mount image is not containing binfmt_misc mountpoint,
add temporary mountpoint to mount tree and try to restore
binfmt_misc content in ordinary way. Then, umount temporary mountpoint.

v4: New
v5: Check for opts.has_binfmt_misc to determine if image presents
v6: Check for binfmt_misc_list to determine if binfmt_misc entries present
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>