add 7.6.0 to the azure devops pipeline

[Mpdreamz]

No description provided.

[Mpdreamz]

Failure on latest-7

Relates to: #4011

[xUnit.net 00:04:16.8305315]     Tests.Modules.SnapshotAndRestore.Repositories.GetRepository.GetRepositoryApiTests.ReturnsExpectedResponse [FAIL]
[xUnit.net 00:04:16.8356939]     Tests.Modules.SnapshotAndRestore.Repositories.GetRepository.GetRepositoryApiTests.ReturnsExpectedIsValid [FAIL]
[xUnit.net 00:04:16.8371526]     Tests.Modules.SnapshotAndRestore.Repositories.GetRepository.GetRepositoryApiTests.ReturnsExpectedStatusCode [FAIL]
[2020-02-24T11:13:34,495][INFO ][o.e.c.s.IndexScopedSettings] [writable-node-706ece9200] [nest-initializer-59d9cc54] updating [index.search.throttled] from [true] to [false]
[2020-02-24T11:13:34,511][INFO ][o.e.c.m.MetaDataCreateIndexService] [writable-node-706ece9200] [nest-fluent-8f725346] creating index, cause [api], templates [nest_tests], shards [1]/[0], mappings [_doc]
[2020-02-24T11:13:34,808][INFO ][o.e.c.m.MetaDataIndexStateService] [writable-node-706ece9200] opening indices [[nest-initializer-59d9cc54/aUN613D0SzuHFRXAwv0wcw]]
[2020-02-24T11:13:35,356][INFO ][o.e.c.m.MetaDataDeleteIndexService] [writable-node-706ece9200] [test-icutransformtests-initializerasync-49bf77b3/YYHxcKe-S9Si2_bh7LqZmQ] deleting index
  X Tests.Modules.SnapshotAndRestore.Repositories.GetRepository.GetRepositoryApiTests.ReturnsExpectedResponse [31s 38ms]
  Error Message:
   System.Exception : Error in integration setup: Invalid NEST response built from a unsuccessful (503) low level call on PUT: /_snapshot/nest-fluentasync-0caa19b3?pretty=true&error_trace=true
# Audit trail of this API call:
 - [1] BadResponse: Node: http://localhost:9200/ Took: 00:00:30.0274608
# OriginalException: Elasticsearch.Net.ElasticsearchClientException: Request failed to execute. Call: Status code 503 from: PUT /_snapshot/nest-fluentasync-0caa19b3?pretty=true&error_trace=true. ServerError: Type: process_cluster_event_timeout_exception Reason: "failed to process cluster event (put_repository [nest-fluentasync-0caa19b3]) within 30s"
# Request:
{"type":"source","settings":{"delegate_type":"fs","chunk_size":"64mb","compress":true,"concurrent_streams":5,"location":"some/location","max_restore_bytes_per_second":"100mb","max_snapshot_bytes_per_second":"200mb"}}
# Response:
{
  "error" : {
    "root_cause" : [
      {
        "type" : "process_cluster_event_timeout_exception",
        "reason" : "failed to process cluster event (put_repository [nest-fluentasync-0caa19b3]) within 30s",
        "stack_trace" : "ProcessClusterEventTimeoutException[failed to process cluster event (put_repository [nest-fluentasync-0caa19b3]) within 30s]\r\n\tat org.elasticsearch.cluster.service.MasterService$Batcher.lambda$onTimeout$0(MasterService.java:143)\r\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1507)\r\n\tat org.elasticsearch.cluster.service.MasterService$Batcher.lambda$onTimeout$1(MasterService.java:142)\r\n\tat org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:633)\r\n\tat java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)\r\n\tat java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)\r\n\tat java.base/java.lang.Thread.run(Thread.java:830)\r\n"
      }
    ],
    "type" : "process_cluster_event_timeout_exception",
    "reason" : "failed to process cluster event (put_repository [nest-fluentasync-0caa19b3]) within 30s",
    "stack_trace" : "ProcessClusterEventTimeoutException[failed to process cluster event (put_repository [nest-fluentasync-0caa19b3]) within 30s]\r\n\tat org.elasticsearch.cluster.service.MasterService$Batcher.lambda$onTimeout$0(MasterService.java:143)\r\n\tat java.base/java.util.ArrayList.forEach(ArrayList.java:1507)\r\n\tat org.elasticsearch.cluster.service.MasterService$Batcher.lambda$onTimeout$1(MasterService.java:142)\r\n\tat org.elasticsearch.common.util.concurrent.ThreadContext$ContextPreservingRunnable.run(ThreadContext.java:633)\r\n\tat java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)\r\n\tat java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)\r\n\tat java.base/java.lang.Thread.run(Thread.java:830)\r\n"
  },
  "status" : 503
}