fix describe mount targets

lib/fog/aws/efs.rb

@@ -159,6 +159,8 @@ module Fog
             raise Fog::AWS::EFS::IncorrectFileSystemLifeCycleState.slurp(error, match[:message])
           elsif match[:code] == 'FileSystemInUse'
             raise Fog::AWS::EFS::FileSystemInUse.slurp(error, match[:message])
+          elsif match[:code] == 'MountTargetNotFound'
+            raise Fog::AWS::EFS::NotFound.slurp(error, match[:message])
           end
           raise case match[:message]
                 when /invalid ((file system)|(mount target)|(security group)) id/i

lib/fog/aws/requests/efs/describe_mount_targets.rb

@@ -39,7 +39,7 @@ module Fog
                             if mount_target = self.data[:mount_targets][id]
                               [mount_target]
                             else
-                              raise Fog::AWS::EFS::NotFound.new("invalid file system ID: #{id}")
+                              raise Fog::AWS::EFS::NotFound.new("Mount target does not exist.")
                             end
                           elsif file_system_id = options[:file_system_id]
                             self.data[:mount_targets].values.select { |mt| mt["FileSystemId"] == file_system_id }

tests/requests/efs/file_system_tests.rb

@@ -105,6 +105,10 @@ Shindo.tests('AWS::EFS | file systems', ['aws', 'efs']) do
       Fog::AWS[:efs].describe_mount_targets(:id => mount_target_id).body
     end
 
+    raises(Fog::AWS::EFS::NotFound, 'Mount target does not exist.') do
+      Fog::AWS[:efs].describe_mount_targets(:id => "foobar")
+    end
+
     raises(Fog::AWS::EFS::Error, 'file system ID or mount target ID must be specified') do
       Fog::AWS[:efs].describe_mount_targets
     end