Fix exception class, message in unit test

Author: mwjones-aws

test/instance_agent/file_credentials_test.rb

@@ -1,4 +1,5 @@
 require 'test_helper'
+require 'aws-sdk-core'
 
 class FileCredentialsTest < InstanceAgentTestCase
   context 'With the file credentials' do
@@ -52,7 +53,7 @@ class FileCredentialsTest < InstanceAgentTestCase
     end
 
     should 'raise error when credential file is missing' do
-      assert_raised_with_message("Failed to load credentials from path #{credentials_path}", RuntimeError) do
+      assert_raised_with_message("Profile `default' not found in #{credentials_path}", Aws::Errors::NoSuchProfileError) do
         InstanceAgent::FileCredentials.new(credentials_path)
       end
     end