China region name is `cn-north-1`.

Closes #156.

Commit ea9609c does not work as expected.

China is not part of the [S3 regions](http://docs.aws.amazon.com/general/latest/gr/rande.html#s3_region) but part of [Isolated Regions](http://docs.aws.amazon.com/general/latest/gr/isolated_regions.html).

The patch uses for S3 `s3-cn-north-1.amazonaws.com` which is wrong because in that case the end point is `s3.cn-north-1.amazonaws.com.cn`.
Same goes for EC2 which was `ec2.cn-north-1.amazonaws.com` but should be `ec2.cn-north-1.amazonaws.com.cn`.

Related documentation:

* http://docs.aws.amazon.com/general/latest/gr/rande.html#s3_region
* http://docs.aws.amazon.com/general/latest/gr/rande.html#ec2_region
* http://docs.aws.amazon.com/general/latest/gr/isolated_regions.html

Closing #156
(cherry picked from commit 491a59b)
(cherry picked from commit f12cacc)

Group LT would like to claim elastic#23720

Support for Role Mapping

Improve conf to allow for dedicated read and write resource as oppose to
a single, unified resource used for both. This allows for different ES
indices to be used in the same index, one as a source and the other as
a sink.

'es.resource' is still supported and used as a fall back.
Higher level abstractions, such as Cascading, Hive and Pig, set the
proper property automatically.

fix elastic#156
fix elastic#45
fix elastic#26

🤖 ESQL: Merge upstream

As disks changed with elastic/infra#16386
update the methodology changelog.