KAFKA-3831; Prepare for updating new-consumer-based Mirror Maker's default partition assignment strategy to round robin
KAFKA-3831; Prepare for updating new-consumer-based Mirror Maker's default partition assignment strategy to round robin

This patch adds proper warning message and necessary doc updates for updating the default partition assignment strategy of Mirror Maker from range to round robin. The actual switch would occur as part of a major release cycle (to be scheduled).

Author: Vahid Hashemian <vahidhashemian@us.ibm.com>

Reviewers: Jason Gustafson <jason@confluent.io>

Closes #1499 from vahidhashemian/KAFKA-3831

Ishiihara/kafka,apache/kafka,mihbor/kafka,ollie314/kafka,Ishiihara/kafka,airbnb/kafka,noslowerdna/kafka,themarkypantz/kafka,sslavic/kafka,rhauch/kafka,rhauch/kafka,noslowerdna/kafka,KevinLiLu/kafka,noslowerdna/kafka,lindong28/kafka,KevinLiLu/kafka,gf53520/kafka,richhaase/kafka,richhaase/kafka,mihbor/kafka,themarkypantz/kafka,lindong28/kafka,Chasego/kafka,ErikKringen/kafka,guozhangwang/kafka,guozhangwang/kafka,gf53520/kafka,ollie314/kafka,ErikKringen/kafka,noslowerdna/kafka,apache/kafka,Chasego/kafka,themarkypantz/kafka,richhaase/kafka,sebadiaz/kafka,geeag/kafka,airbnb/kafka,Esquive/kafka,MyPureCloud/kafka,ijuma/kafka,ijuma/kafka,sebadiaz/kafka,lindong28/kafka,eribeiro/kafka,mihbor/kafka,TiVo/kafka,MyPureCloud/kafka,Chasego/kafka,TiVo/kafka,KevinLiLu/kafka,eribeiro/kafka,sslavic/kafka,mihbor/kafka,sslavic/kafka,geeag/kafka,ollie314/kafka,Ishiihara/kafka,Ishiihara/kafka,guozhangwang/kafka,ijuma/kafka,Esquive/kafka,geeag/kafka,ollie314/kafka,apache/kafka,MyPureCloud/kafka,Esquive/kafka,lindong28/kafka,sebadiaz/kafka,TiVo/kafka,Esquive/kafka,KevinLiLu/kafka,sslavic/kafka,gf53520/kafka,apache/kafka,ijuma/kafka,TiVo/kafka,rhauch/kafka,eribeiro/kafka,airbnb/kafka,gf53520/kafka,MyPureCloud/kafka,airbnb/kafka,ErikKringen/kafka,themarkypantz/kafka,sebadiaz/kafka,guozhangwang/kafka,rhauch/kafka,geeag/kafka,richhaase/kafka,ErikKringen/kafka,eribeiro/kafka,Chasego/kafka