[ISSUE #1678] Use thread safe CopyOnWriteArrayList for registerBrokerResultList

[lich0079]

What is the purpose of the change

registerBrokerResultList will invoke add in separate threads, therefore it's not safe to use ArrayList, fix #1678

Brief changelog

Follow existing code pattern https://github.com/apache/rocketmq/blob/master/broker/src/main/java/org/apache/rocketmq/broker/out/BrokerOuterAPI.java#L268
to use thread-safe CopyOnWriteArrayList

Verifying this change

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[xujianhai666]

@lich0079 ci failed, more info /home/travis/build/apache/rocketmq/broker/src/main/java/org/apache/rocketmq/broker/out/BrokerOuterAPI.java:19:8: error: Unused import - com.google.common.collect.Lists.

[coveralls]

Coverage increased (+0.03%) to 50.901% when pulling 804c189 on lich0079:issue_1678 into 997164b on apache:develop.

[lich0079]

@xujianhai666 code updated, please check.