OPENDJ-2776 Remove trailing spaces from AVAs and RDNs during parsing

Leading and trailing whitespace in RDN attribute values must be escaped
according to RFC 4514, otherwise the RDN is invalid. However, it is
often best practice to be tolerant of malformed data, so we should
really trim off any leading or trailing whitespaces. The AVA class was
already trimming leading whitespace, but not trailing.