Don't AddError for Rollback on ErrTxDone

[j16r]

When db.Rollback fails, check the error code. If it matches sql.ErrTxDone, we won't treat it as an error. This is expected and normal behavior of using Rollback with defer.

e.g:

tx := db.Begin()
defer tx.Rollback()
...
return tx.Commit().Error

See more discussion here: go-gormigrate/gormigrate#36

[codecov-io]

Codecov Report

Merging #2434 into master will decrease coverage by 0.05%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master   #2434      +/-   ##
=========================================
- Coverage   80.15%   80.1%   -0.06%     
=========================================
  Files          24      24              
  Lines        3432    3433       +1     
=========================================
- Hits         2751    2750       -1     
- Misses        578     580       +2     
  Partials      103     103

Impacted Files	Coverage Δ
main.go	82.58% <0%> (-0.46%)	⬇️

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[j16r]

@javie2007 what do you think it would take to get this merged? The coverage could be a little tricky, not sure how to trigger an appropriate error in Rollback.

[andreynering]

Ping @jinzhu @emirb