This fix tries to address the issue raised in 29344 where it was
not possible to create log group for awslogs (CloudWatch) on-demand.
Log group has to be created explicitly before container is running.
This behavior is inconsistent with AWS logs agent where log groups
are always created as needed.
There were several concerns previously (See comments in 19617 and 29344):
1. There is a limit of 500 log groups/account/region so resource might
be exhausted if there is any typo or incorrect region.
2. Logs are generated for every container so CreateLogGroup (or equally,
DescribeLogGroups) might be called every time, which is redundant and
potentially surprising.
3. CreateLogStream and CreateLogGroup have different IAM policies.
This fix addresses the issue by add `--log-opt awslogs-create-group`
which by default is `false`. It requires user to explicitly request
that log groups be created as needed.
Related unit test has been updated. And tests have also been done
manually in AWS.
This fix fixes 29334.
Signed-off-by: Yong Tang <yong.tang.github@outlook.com>
