ec2_lc.py: Also pass 'encrypted' when adding a volume

This only allows for using the default KMS keys, but enables encryption
at rest without needing to migrate the module to boto3

lib/ansible/modules/cloud/amazon/ec2_lc.py

@@ -140,6 +140,7 @@ EXAMPLES = '''
       device_type: io1
       iops: 3000
       delete_on_termination: true
+      encrypted: true
     - device_name: /dev/sdb
       ephemeral: ephemeral0
 
@@ -177,7 +178,8 @@ def create_block_device(module, volume):
                            size=volume.get('volume_size'),
                            volume_type=volume.get('device_type'),
                            delete_on_termination=volume.get('delete_on_termination', False),
-                           iops=volume.get('iops'))
+                           iops=volume.get('iops'),
+                           encrypted=volume.get('encrypted',None))
 
 
 def create_launch_config(connection, module):