Pass list of numbers to comma_delimited_list breaks

[hongbin]

Here is the step to reproduce:

* The template and environment file:

$ cat test.yaml
heat_template_version: 2014-10-16
parameters:
  test:
    type: comma_delimited_list
    default: []
resources:
  random_group:
    type: OS::Heat::ResourceGroup
    properties:
      count: 5
      removal_policies: [{resource_list: {get_param: test}}]
      resource_def:
        type: OS::Heat::RandomString

$ cat local.yaml
parameters:
  test: [0]

* Create a stack succeeded

$ heat stack-create -f test.yaml test
+--------------------------------------+------------+--------------------+---------------------+
| id | stack_name | stack_status | creation_time |
+--------------------------------------+------------+--------------------+---------------------+
| 43124748-b2f8-4522-a1b8-91075d7b1828 | test | CREATE_IN_PROGRESS | 2015-06-20T15:05:14 |

+--------------------------------------+------------+--------------------+---------------------+

$ heat stack-list
+--------------------------------------+------------+-----------------+---------------------+
| id | stack_name | stack_status | creation_time |
+--------------------------------------+------------+-----------------+---------------------+
| 43124748-b2f8-4522-a1b8-91075d7b1828 | test | CREATE_COMPLETE | 2015-06-20T15:05:14 |
+--------------------------------------+------------+-----------------+---------------------+

* Update the stack with list of numbers as parameter accepted, and sub-sequence requests failed.

$ heat stack-update -f test.yaml -e local.yaml test
+--------------------------------------+------------+-----------------+---------------------+
| id | stack_name | stack_status | creation_time |
+--------------------------------------+------------+-----------------+---------------------+
| 43124748-b2f8-4522-a1b8-91075d7b1828 | test | CREATE_COMPLETE | 2015-06-20T15:05:14 |
+--------------------------------------+------------+-----------------+---------------------+

$ heat stack-list
ERROR: The server could not comply with the request since it is either malformed or otherwise incorrect.

* Here is the server trace:

2015-06-20 11:05:47.263 ERROR oslo_messaging.rpc.dispatcher [req-d78a6e4f-dd5f-4f8b-b60f-0b6546ee07e3 None demo] Exception during message handling: sequence item 0: expected string, int found
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher Traceback (most recent call last):
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 142, in _dispatch_and_reply
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher executor_callback))
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 186, in _dispatch
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher executor_callback)
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/usr/local/lib/python2.7/dist-packages/oslo_messaging/rpc/dispatcher.py", line 130, in _do_dispatch
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher result = func(ctxt, **new_args)
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/usr/local/lib/python2.7/dist-packages/osprofiler/profiler.py", line 105, in wrapper
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher return f(*args, **kwargs)
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/opt/stack/heat/heat/common/context.py", line 267, in wrapped
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher return func(self, ctx, *args, **kwargs)
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/opt/stack/heat/heat/engine/service.py", line 511, in list_stacks
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher return [api.format_stack(stack) for stack in stacks]
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/opt/stack/heat/heat/engine/api.py", line 120, in format_stack
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher rpc_api.STACK_PARAMETERS: stack.parameters.map(str),
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/opt/stack/heat/heat/engine/parameters.py", line 519, in map
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher for n, p in six.iteritems(self.params) if filter_func(p))
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/opt/stack/heat/heat/engine/parameters.py", line 519, in <genexpr>
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher for n, p in six.iteritems(self.params) if filter_func(p))
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher File "/opt/stack/heat/heat/engine/parameters.py", line 384, in __str__
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher return ",".join(self.value())
2015-06-20 11:05:47.263 TRACE oslo_messaging.rpc.dispatcher TypeError: sequence item 0: expected string, int found