According to the AWS documentation
(https://docs.aws.amazon.com/AmazonS3/latest/API/API_GetBucketPolicyStatus.html),
the `IsPublic` tag value should be in uppercase. However, the `aws-cli`
utility interprets such responses as always `false`.
To avoid incorrect interpretation, we now return the tag value in lowercase.
Signed-off-by: Aleksey Kravchenko <al.kravchenko@yadro.com>
d85e5b10bb