Bulk-operation without index/type

Bulk-operations is not working if elasticsearch settings
rest.action.multi.allow_explicit_index
Update tests for bulk-update with FixedPath to work if even if the _index attribute not are allowed
Update tests for multiperculate with FixedPath to work if even if the _index attribute not are allowed
Update tests for multisearch with FixedPath to work if even if the _index attribute not are allowed
Update tests forMultiSearch with FixedPath to work if even if the index attribute not are allowed
Update serializer for Bulk, MultiSearch and MultiPercolate to ignore index-parameter if that is the same as FixedPath
Correcting BulkIndexDetailsFixedPath test
Merge branch 'issue-870' of github.com:Tasteful/elasticsearch-net into Tasteful-issue-870

Conflicts:
	src/Tests/Nest.Tests.Integration/Core/Bulk/BulkUpdateTests.cs
reverted @Tasteful fixes to tests so they work with rest.action.multi.allow_explicit_index set to false, nest tests should serve as documentation for vanilla elasticsearch installs otherwise FixedIndex() might be taken for mandatory
Merge branch 'develop' of github.com:elasticsearch/elasticsearch-net into develop