p2p, log, rpc: use errors.New to replace fmt.Errorf with no parameter…

[ucwong]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 1 lines in your changes are missing coverage. Please review.

Project coverage is 47.44%. Comparing base (ee90131) to head (ad87771).
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1920      +/-   ##
==========================================
+ Coverage   47.39%   47.44%   +0.04%     
==========================================
  Files         568      568              
  Lines       68782    68782              
==========================================
+ Hits        32601    32633      +32     
+ Misses      33645    33605      -40     
- Partials     2536     2544       +8     

Files	Coverage Δ
p2p/transport.go	82.66% <100.00%> (ø)
rpc/types.go	76.47% <100.00%> (ø)
p2p/server.go	72.57% <50.00%> (ø)

... and 16 files with indirect coverage changes