Print set config values on node start

[cyberj0g]

As discussed in #2613, echo non-nil fields of config object, which changed with CLI arguments, config file or environment variables.

[codecov]

Codecov Report

Merging #2616 (45bd8c8) into master (dc6e79d) will decrease coverage by 0.04176%.
The diff coverage is 0.00000%.

@@                 Coverage Diff                 @@
##              master       #2616         +/-   ##
===================================================
- Coverage   56.44931%   56.40755%   -0.04176%     
===================================================
  Files             88          88                 
  Lines          18909       18923         +14     
===================================================
  Hits           10674       10674                 
- Misses          7656        7670         +14     
  Partials         579         579                 

Impacted Files	Coverage Δ
cmd/livepeer/livepeer.go	47.28261% <0.00000%> (-3.89387%)	⬇️

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Impacted Files	Coverage Δ
cmd/livepeer/livepeer.go	47.28261% <0.00000%> (-3.89387%)	⬇️

[iameli]

Reverting — this breaks livepeer -j by returning a bunch of non-JSON that MistController can't parse when it's booting up

[iameli]

Reverting — this breaks livepeer -j by returning a bunch of non-JSON that MistController can't parse when it's booting up