[#603] Fix GetBucketPolicyStatus case sensitivity

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>

api/handler/response.go

@@ -67,9 +67,12 @@ type PolicyStatus struct {
 
 type PolicyStatusIsPublic string
 
+// 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 return the tag value in lowercase.
 const (
-	PolicyStatusIsPublicFalse = "FALSE"
-	PolicyStatusIsPublicTrue  = "TRUE"
+	PolicyStatusIsPublicFalse = "false"
+	PolicyStatusIsPublicTrue  = "true"
 )
 
 // AccessControlPolicy contains ACL.