[tests] split index 7-SNAPSHOT

[Mpdreamz]

build.bat seed:98745 integrate latest-7 "writable" "splitindex"

From: #4004

  "acknowledged" : true,
  "shards_acknowledged" : false,

out tests assume shards_acknowledge is always true, sometimes this is not the case.

[xUnit.net 00:06:45.9486021]     Tests.Indices.IndexManagement.SplitIndex.SplitIndexApiTests.ReturnsExpectedResponse [FAIL]
Failed   Tests.Indices.IndexManagement.SplitIndex.SplitIndexApiTests.ReturnsExpectedResponse
Error Message:
 Tests.Framework.EndpointTests.ResponseAssertionException : Expected response.ShardsAcknowledged to be true, but found False.
Response Under Test:
Valid NEST response built from a successful (200) low level call on PUT: /nest-fluentasync-77a092ae/_split/nest-fluentasync-77a092ae-target?pretty=true&error_trace=true
# Audit trail of this API call:
 - [1] HealthyResponse: Node: http://localhost:9200/ Took: 00:00:30.5230768
# Request:
{"settings":{"index.number_of_shards":8}}
# Response:
{
  "acknowledged" : true,
  "shards_acknowledged" : false,
  "index" : "nest-fluentasync-77a092ae-target"
}