Add some tests to increase code coverage

[chu11]

Added tests for flux_lspeer(), flux_rmmod(), flux_lsmod(), and flux_insmod().

A couple of minor cleanups along the way.

[coveralls]

Coverage increased (+0.3%) to 77.947% when pulling d7cbad1 on chu11:coverage into 2d3820a on flux-framework:master.

[codecov-io]

Codecov Report

Merging #1011 into master will increase coverage by 0.33%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master    #1011      +/-   ##
==========================================
+ Coverage   77.29%   77.63%   +0.33%     
==========================================
  Files         151      151              
  Lines       25751    25751              
==========================================
+ Hits        19905    19992      +87     
+ Misses       5846     5759      -87

Impacted Files	Coverage Δ
src/cmd/flux-comms.c	43.13% <0%> (+7.84%)	✅
src/modules/kvs/kvs.c	80.59% <0%> (-0.25%)	❌
src/common/libflux/message.c	83.39% <0%> (-0.13%)	❌
src/broker/broker.c	70.63% <0%> (+0.38%)	✅
src/common/libflux/handle.c	86.04% <0%> (+0.51%)	✅
src/broker/overlay.c	71.06% <0%> (+1.88%)	✅
src/common/libflux/module.c	79.26% <0%> (+29.95%)	✅
src/common/libflux/reparent.c	42.85% <0%> (+42.85%)	✅

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[chu11]

77.947% ... so close :-)

[garlick]

Thanks! Merging.