Fix spot instance creation by ignoring instance_initiated_shutdown_behavior (#4741)

Before this, all spot instance requests would fail because the code
_always_ called module.fail_json when the parameter was set (which it
always was, because the module parameter's default was set to 'stop').

As the comment said, this parameter doesn't make sense for spot
instances at all, so the error message was also misleading.

lib/ansible/modules/cloud/amazon/ec2.py

@@ -1048,8 +1048,9 @@ def create_instances(module, ec2, vpc, override_count=None):
                       private_ip_address = private_ip,
                     ))
 
-                # Spot instances do not support start/stop thereby not having the option to change shutdown behavior
-                params['instance_initiated_shutdown_behavior'] = instance_initiated_shutdown_behavior
+                # For ordinary (not spot) instances, we can select 'stop'
+                # (the default) or 'terminate' here.
+                params['instance_initiated_shutdown_behavior'] = instance_initiated_shutdown_behavior or 'stop'
 
                 res = ec2.run_instances(**params)
                 instids = [ i.id for i in res.instances ]
@@ -1085,11 +1086,11 @@ def create_instances(module, ec2, vpc, override_count=None):
                         module.fail_json(
                             msg="placement_group parameter requires Boto version 2.3.0 or higher.")
 
-                if boto_supports_param_in_spot_request(ec2, 'instance_initiated_shutdown_behavior'):
-                    params['instance_initiated_shutdown_behavior'] = instance_initiated_shutdown_behavior
-                elif instance_initiated_shutdown_behavior:
+                # You can't tell spot instances to 'stop'; they will always be
+                # 'terminate'd. For convenience, we'll ignore the latter value.
+                if instance_initiated_shutdown_behavior and instance_initiated_shutdown_behavior != 'terminate':
                     module.fail_json(
-                        msg="instance_initiated_shutdown_behavior parameter is not supported by your Boto version.")
+                        msg="instance_initiated_shutdown_behavior=stop is not supported for spot instances.")
 
                 if spot_launch_group and isinstance(spot_launch_group, basestring):
                     params['launch_group'] = spot_launch_group
@@ -1452,7 +1453,7 @@ def main():
             source_dest_check = dict(type='bool', default=True),
             termination_protection = dict(type='bool', default=False),
             state = dict(default='present', choices=['present', 'absent', 'running', 'restarted', 'stopped']),
-            instance_initiated_shutdown_behavior=dict(default='stop', choices=['stop', 'terminate']),
+            instance_initiated_shutdown_behavior=dict(default=None, choices=['stop', 'terminate']),
             exact_count = dict(type='int', default=None),
             count_tag = dict(),
             volumes = dict(type='list'),