Remove assertion when there is an error in Presto

[timifasubaa]

The new schema for response_json in Presto 0.166 contains nextUri and this assertion prevents useful error messages in response['error'] from being propagated when errors happen. Instead it sends "Should not have nextUri if failed" which is not a useful error message.
@jingw

[mistercrunch]

For context please specify which version of Presto where the issue has been identified.

[codecov-io]

Codecov Report

Merging #164 into master will decrease coverage by <.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #164      +/-   ##
==========================================
- Coverage   95.68%   95.68%   -0.01%     
==========================================
  Files          14       14              
  Lines        1415     1414       -1     
  Branches      146      146              
==========================================
- Hits         1354     1353       -1     
  Misses         40       40              
  Partials       21       21

Impacted Files	Coverage Δ
pyhive/presto.py	93.61% <ø> (-0.05%)	⬇️

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[matthewwardrop]

@jingw Greetings again!

Just pinging you about this PR in case you hadn't seen it. According to the official docs, insofar as you can call them that, the nextUri may or may not be present on any response, and one should just rely on the error field to determine whether there has been an error. As far as I can see there is no mention of nextUri being missing for errors. This is only masking error messages for true issues, so it is at least not preventing queries from succeeding, but it has made it hard to diagnose some users' issues.

Any chance you could consider merging this in soon?

[jingw]

lgtm, thank you! sorry for the delay.

[matthewwardrop]

Thanks @jingw !

[matthewwardrop]

@jingw Would be great to get this pushed out in a point release if possible :).