test: TestDeleteOffsetsResponse is brittle and fails periodically

[dnwe]

The new TestDeleteOffsetsResponse looks like it can fail periodically due to a timing issue:

% go test -run 'TestDeleteOffsetsResponse' -v -count=10
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
    request_test.go:96: Encoding no error failed
        got  [0 0 0 0 0 0 0 0 0 1 0 3 98 97 114 0 0 0 2 0 0 0 7 0 0 0 0 0 6 0 0]
        want [0 0 0 0 0 0 0 0 0 1 0 3 98 97 114 0 0 0 2 0 0 0 6 0 0 0 0 0 7 0 0]
--- FAIL: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
=== RUN   TestDeleteOffsetsResponse
--- PASS: TestDeleteOffsetsResponse (0.00s)
FAIL
exit status 1
FAIL    github.com/Shopify/sarama       0.361s

Needs investigating if we can make it more robust.

cc @faillefer

[dnwe]

Ah it's the randomised ordering of the map of partitions in the response

[faillefer]

@dnwe
Maybe the best correction is to sort by partition when encoding the response. So the result will always be the same.
I can provide a fix