Add test for disabling commit-merge in kvs + additional minor cleanup patches

[chu11]

Test for disabling commit-merge in kvs per discussion in issue #813

[coveralls]

Coverage increased (+0.01%) to 76.193% when pulling ce06972 on chu11:issue813-unittest into edc914e on flux-framework:master.

[codecov-io]

Codecov Report

Merging #979 into master will increase coverage by 0.01%.

@@            Coverage Diff             @@
##           master     #979      +/-   ##
==========================================
+ Coverage    75.9%   75.91%   +0.01%     
==========================================
  Files         152      152              
  Lines       25937    25937              
==========================================
+ Hits        19688    19691       +3     
+ Misses       6249     6246       -3

Impacted Files	Coverage Δ
src/broker/module.c	78.82% <100%> (ø)	✅
src/broker/modservice.c	63.15% <ø> (-0.88%)	❌
src/common/libutil/veb.c	98.29% <ø> (-0.57%)	❌
src/common/libflux/message.c	83.44% <ø> (-0.14%)	❌
src/common/libflux/dispatch.c	82.71% <ø> (+0.28%)	✅
src/modules/kvs/kvs.c	80.46% <ø> (+0.36%)	✅
src/modules/kvs/waitqueue.c	88.17% <ø> (+2.15%)	✅

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[garlick]

Sounds good. Is this ready to go?

[chu11]

yup!