reduce max mongo bulk ops to 1000

[trinchan]

Prior to Mongo 3.5, the max bulk op size is 1000. In latest versions, it looks like it is configurable by the server. Future work could be to detect version and configured max bulk op size and set appropriately. (mgo should really be doing this...)

Commit which shows bulk op size: mongodb/mongo@5032874

[codecov]

Codecov Report

Merging #450 into master will increase coverage by 0.44%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #450      +/-   ##
==========================================
+ Coverage   85.92%   86.36%   +0.44%     
==========================================
  Files          61       61              
  Lines        3587     3587              
==========================================
+ Hits         3082     3098      +16     
+ Misses        334      320      -14     
+ Partials      171      169       -2

Impacted Files	Coverage Δ
adaptor/mongodb/bulk.go	80% <ø> (ø)	⬆️
adaptor/elasticsearch/clients/v5/writer.go	88.65% <0%> (+8.24%)	⬆️
adaptor/elasticsearch/clients/v2/writer.go	86.07% <0%> (+10.12%)	⬆️

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[burhaanw16]

Hello Everyone, I am syncing data between two mongodbs using transporter and my MongoDB version is 3.4.24. Since the max write batch size limit of that version is 1000, I am getting an error while using Transporter with details as:-
"flush error, Write batch sizes must be between 1 and 1000. Got 1398 operations".
Can anyone please help me in bypassing this error.