Wrong representation of Attributes

[Sergey Kraynev]

If you try to display Attributes class during debugging or via str() function you will get follow traceback:

  File "heat/engine/attributes.py", line 236, in __repr__
    '\n\t'.join(six.itervalues(self._attributes)))
TypeError: sequence item 0: expected string, Attribute found

It happens due to "join" expect list, but six.itervalues(self._attributes) returns Attribute classes. To fix it we need to use just "self"
instead of self._attributes.

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/200059
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=658d61ecee175036b81b0c6897587c0506a07679
Submitter: Jenkins
Branch: master

commit 658d61ecee175036b81b0c6897587c0506a07679
Author: Sergey Kraynev <email address hidden>
Date: Thu Jul 9 08:48:21 2015 -0400

    Use __iter__ method of Attributes class in __repr__ method

    Join method expects list, but six.itervalues(self._attributes) returns
    a Attribute instance, so we should use own __iter__ method for building
    list of values.

    Closes-Bug: #1473974

    Change-Id: I7c5d4a5a8d0142156c3416347940b9e90ed8df5c