[FINE] Do not downcase the amazon IAM username

(manually picked from ManageIQ/manageiq-providers-amazon@3a2408b)

The code has been refactored on the master branch. It has been moved to
the https://github.com/ManageIQ/manageiq-providers-amazon repository.

The master PR for this change is:
ManageIQ/manageiq-providers-amazon#296

This commit addresses:
https://bugzilla.redhat.com/show_bug.cgi?id=1489596

app/models/authenticator/amazon.rb

@@ -133,5 +133,9 @@ def aws_connect(access_key_id, secret_access_key, service = :IAM, proxy_uri = ni
         :log_formatter     => Aws::Log::Formatter.new(Aws::Log::Formatter.default.pattern.chomp)
       )
     end
+
+    def normalize_username(username)
+      username
+    end
   end
 end

spec/models/authenticator/amazon_spec.rb

@@ -1,8 +1,8 @@
 require 'aws-sdk'
 
 describe Authenticator::Amazon do
-  AWS_ROOT_USER_KEY = 'aws_root_key'
-  AWS_IAM_USER_KEY = 'aws_iam_key'
+  AWS_ROOT_USER_KEY = 'aws_root_key'.freeze
+  AWS_IAM_USER_KEY = 'AWS_IAM_KEY'.freeze
 
   subject { Authenticator::Amazon.new(config) }