Fix issue with non str, non Exception type failure messages

[cyberw]

No description provided.

[codecov]

Codecov Report

Merging #1517 into master will decrease coverage by 0.12%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1517      +/-   ##
==========================================
- Coverage   81.34%   81.22%   -0.13%     
==========================================
  Files          27       27              
  Lines        2391     2391              
  Branches      368      368              
==========================================
- Hits         1945     1942       -3     
- Misses        353      356       +3     
  Partials       93       93              

Impacted Files	Coverage Δ
locust/clients.py	90.19% <0.00%> (-4.91%)	⬇️
locust/contrib/fasthttp.py	85.44% <0.00%> (ø)
locust/runners.py	80.61% <0.00%> (-0.21%)	⬇️
locust/user/task.py	97.29% <0.00%> (+1.62%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 0a0b273...7953ad9. Read the comment docs.