Add a new exception for MongoDB Authentication errors

[lavinasachdev3]

Fixes issue #1336

Have used 'Authentication fail' as the comparison string for authentication failure so that we are able to handle both 'Authentication failed' and 'Authentication failure' error messages.
Also, was thinking of comparing the strings ignoring the case so that if mongo changes their return text to Authentication Fail, it still works. Should we do that or does it seem unnecessary?

[codecov-io]

Codecov Report

Merging #1357 into master will decrease coverage by 0.03%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #1357      +/-   ##
==========================================
- Coverage   98.19%   98.16%   -0.04%     
==========================================
  Files          54       54              
  Lines        2444     2447       +3     
==========================================
+ Hits         2400     2402       +2     
- Misses         44       45       +1

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[ttmc]

Hi @lavinasachdev3,

(Sorry I didn't post this message earlier. I usually do so quicker, but I was away on vacation last week and didn't notice your two recent pull requests until now.)

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[lavinasachdev3]

Sent the agreement.

[lavinasachdev3]

This is to confirm that I agreed to and accepted the BigchainDB Individual Contributor Agreement at https://www.bigchaindb.com/cla/ and to represent and warrant that I have authority to do so.

CuQ2H2InIi8OlYnbBMBlRM0XXOza2RcPcAoRwFbCM47zDUvAVhXmrKhg5GGAz3u

[ttmc]

Great, thanks @lavinasachdev3

The CLA hurdle is cleared.

[vrde]

Hi @lavinasachdev3, thanks for your PR 🎉

It looks good but, after discussing with the MongoDB folks, I'm undecided if the approach I suggested in #1336 is enough.

I'll wait to know the answer to my question on their issue tracker to decide how to proceed with this PR.

[r-marques]

If after clarifying with the mongodb folks we think that this should go through this pr should add a unit test to test this behaviour.