HOTFIX: Use a true sentinel for `UseDefaultAcls`
HOTFIX: Use a true sentinel for `UseDefaultAcls`

In 67fc2a91a6, we are using an empty collection and comparing via
value equality, so if a user passes an empty collection, they will
get the default ACLs instead of no ACLs. We fix that issue here.

Author: Ismael Juma <ismael@juma.me.uk>

Reviewers: Rajini Sivaram

Closes #2829 from ijuma/zk-utils-default-acls-improvement and squashes the following commits:

0846172 [Ismael Juma] Add missing import
2dc84f3 [Ismael Juma] Simplify logic in `sensitivePath`
8122f27 [Ismael Juma] Use a true sentinel instead of an empty collection for `UseDefaultAcls`

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