Set handleCommandError to WARN

[pm47]

Those are not fatal errors for channels.

[codecov-io]

Codecov Report

Merging #1012 into master will increase coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1012      +/-   ##
==========================================
+ Coverage   80.22%   80.25%   +0.02%     
==========================================
  Files          98       98              
  Lines        7546     7546              
  Branches      291      291              
==========================================
+ Hits         6054     6056       +2     
+ Misses       1492     1490       -2

Impacted Files	Coverage Δ
...c/main/scala/fr/acinq/eclair/channel/Channel.scala	83.59% <100%> (+0.48%)	⬆️
...clair/blockchain/electrum/ElectrumClientPool.scala	74.19% <0%> (-4.31%)	⬇️
...src/main/scala/fr/acinq/eclair/router/Router.scala	85.78% <0%> (-0.95%)	⬇️
.../acinq/eclair/blockchain/bitcoind/ZmqWatcher.scala	97.05% <0%> (+3.92%)	⬆️
...lockchain/bitcoind/rpc/ExtendedBitcoinClient.scala	100% <0%> (+8.33%)	⬆️