doc/man1/flux-kvs: Update language

[chu11]

A number of open source projects have been removing the term "slave" from their lexicon. So to be up with the times, remove "slave" nomenclature that lingered in this manpage.

[coveralls]

Coverage increased (+0.03%) to 78.577% when pulling c5c20af on chu11:masterslaveupdate into 53697fa on flux-framework:master.

[codecov-io]

Codecov Report

Merging #1301 into master will increase coverage by 0.04%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1301      +/-   ##
==========================================
+ Coverage   78.24%   78.28%   +0.04%     
==========================================
  Files         154      154              
  Lines       27935    27935              
==========================================
+ Hits        21857    21869      +12     
+ Misses       6078     6066      -12

Impacted Files	Coverage Δ
src/common/libutil/dirwalk.c	93.57% <0%> (-0.72%)	⬇️
src/bindings/lua/flux-lua.c	81.16% <0%> (+0.08%)	⬆️
src/common/libflux/message.c	81.6% <0%> (+0.11%)	⬆️
src/broker/content-cache.c	74.73% <0%> (+1.29%)	⬆️
src/broker/module.c	85.19% <0%> (+1.39%)	⬆️

[chu11]

build hung after

PASS: t4000-issues-test-driver.t 4 - t0900-wreck-invalid-cores.sh

restarting.

[garlick]

I suggest you go with "leader" and "follower" (or maybe there's a better pair of terms?) instead of rank 0 and rank > 0 since I think the design will need to evolve away from rank 0 specialness. That was the reason for the original language.

[grondo]

I like "follower" which works even if you keep "master".

someone else on the wise internet has suggested primary/secondary or primary/replica, etc.

[chu11]

Ok, lets go with leader & follower. B/c we hadn't established a nomenclature, I just went with "rank 0" and "rank > 0".

[coveralls]

Coverage increased (+0.04%) to 78.584% when pulling dadb04c on chu11:masterslaveupdate into b43aca0 on flux-framework:master.

[chu11]

updated, rebased, and re-pushed

[coveralls]

Coverage increased (+0.03%) to 78.58% when pulling 380c052 on chu11:masterslaveupdate into b43aca0 on flux-framework:master.

[chu11]

rebased on master again

[coveralls]

Coverage increased (+0.04%) to 78.612% when pulling e7c32d8 on chu11:masterslaveupdate into c83814e on flux-framework:master.

[garlick]

Thanks @chu11!