Metadata cache cleared by a full metadata refresh

[emasab]

Description

Metadata cache is cleared if a full metadata request is made, that happens because cache isn't updated by because of this condition and the all entries that haven't been updated since function start are cleared here

How to reproduce

Execute test 0146/do_test_metadata_persists_in_cache in #4677.

Checklist

Please provide the following information:

• librdkafka version (2.1.0)
• Apache Kafka version: <REPLACE with e.g., 0.10.2.3>
• librdkafka client configuration: <REPLACE with e.g., message.timeout.ms=123, auto.reset.offset=earliest, ..>
• Operating system: <REPLACE with e.g., Centos 5 (x64)>
• Provide logs (with debug=.. as necessary) from librdkafka
• Provide broker log excerpts
• Critical issue

[emasab]

Fixed in #4677