Added an option awslogs-create-stream to allow skipping log stream creation for awslogs log driver. The default value is still true to keep the behavior be consistent with before.

Signed-off-by: Xia Wu [email protected]

- What I did
Added a new option awslogs-create-stream to awslogs log driver to allow skipping log stream creation in AWS CloudWatch Logs. It's very similar to awslogs-create-group but used for log stream creation.

- How I did it
Added a new option in awslogs log config map.

- How to verify it

1. Built Docker locally and ran a Docker container with awslogs-create-stream=false with an existed log stream name in AWS CloudWatch Logs, the log stream creation was skipped and container started to run successfully.

docker run -d --command "echo hello" \
   --env xxx (credentials) \
   --log-driver=awslogs  \
   --log-opt awslogs-group=test-group \
   --log-opt awslogs-group=test-stream \
   --log-opt awslogs-region=us-west-2 \
   --log-opt awslogs-create-stream=false \
   busybox:latest 

2. Also ran a Docker container without log option awslogs-create-stream and the log stream created in CloudWatch Logs successfully.
3. Modified existing unit tests and added a unit test for skipped log stream creation.

- Description for the changelog
Added a new option to awslogs log driver to allow skipping log stream creation in AWS CloudWatch Logs.

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