Log libStorage error from logVolumeLoopError

[codenrhoden]

When libStorage would return an error like:

{
  "message": "POST https://api.digitalocean.com/v2/volumes: 422 Storage is not supported for this region",
  "status": 500,
  "error": "POST https://api.digitalocean.com/v2/volumes: 422 Storage is not supported for this region"
}

The only thing printed to the REX-Ray CLI output was
"error.status=500", and not the actual error message. Fix that by
asserting type to goof.HTTPError, then extracting the real message.

Fixes codedellemc/libstorage#429

This ends up being the difference between a final output of:

FATA[0002] error creating volume                         error.status=500 volume=test

vs

FATA[0002] error creating volume                         error.status=500 error.msg=POST https://api.digitalocean.com/v2/volumes: 422 Storage is not supported for this region volume=test

I think the new output is much more helpful

[codenrhoden]

I admit I don't fully understand the interaction between golf, goof, and logrus. I tried for about 90 minutes to figure out why something like log.WithError(httpErr), whereby httpErr was created with httpErr, ok := err.(goof.HTTPErr) wouldn't automatically add error.msg to the log fields. error.status shows up on its own, but no other fields do.

I tried every combination of IncludeFieldsWith{Error,String,Format}, but still no luck. I could log the fields directly that way, by doing log.Debugf("%+v", httpErr), but log.WithError() would never show them.

I still think this is a vast improvement, and actually closes out the Epic #776.

[codecov-io]

Codecov Report

Merging #899 into master will decrease coverage by <.01%.
The diff coverage is 0%.

@@            Coverage Diff            @@
##           master    #899      +/-   ##
=========================================
- Coverage     8.8%   8.79%   -0.01%     
=========================================
  Files          25      25              
  Lines        2977    2980       +3     
=========================================
  Hits          262     262              
- Misses       2679    2682       +3     
  Partials       36      36

Impacted Files	Coverage Δ
cli/cli/cmds_10_volume.go	0.14% <0%> (-0.01%)	⬇️

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