Allow log to pack raw nodes

[vEpiphyte]

• Refactor log command to use synapse.lib.cmd
• Add --nodes-only argument to log to capture only packed nodes to disk.

[codecov]

Codecov Report

Merging #1213 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1213      +/-   ##
==========================================
+ Coverage   93.55%   93.56%   +<.01%     
==========================================
  Files         124      124              
  Lines       16613    16633      +20     
==========================================
+ Hits        15543    15563      +20     
  Misses       1070     1070

Impacted Files	Coverage Δ
synapse/cmds/cortex.py	91.59% <100%> (+0.77%)	⬆️

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