Now owner ID field is not required to be set. According to
latest neofs-api, this field set if token was issued for
specific owner ID. If this field is not set, then any user
can use this token while it is correctly signed and has valid
lifetime.
Lifetime is also can be omitted since node interpret empty
lifetime as a lifetime with zero values.
Signed-off-by: Alex Vanin <alexey@nspcc.ru>