MINOR: Fix delegation token system test (#12693)
MINOR: Fix delegation token system test (#12693)

KIP-373 added a "token requester" field to the output of kafka-delegation-tokens.sh. The system test was failing since it was not expecting this new field. This patch adds support for this field and improves the error output if we can't parse.

Reviewers: José Armando García Sancio <a8f36d709c55b131453e2fdebab89d11b4e5c5e0@apache.org>, Manikumar Reddy <manikumar.reddy@gmail.com>
apache/kafka,apache/kafka,apache/kafka,apache/kafka