server update failed if enable observe_on_update

[huangtianhua]

1. enable observe_on_update
2. create a stack with a nova server
3. update the stack to change name of server
4. stack update failed, the reason is: http://paste.openstack.org/show/592070/

We get the live properties of server, nova returns the response with 'metadata={}', so we update the before_props with it, but after_props with metadata=None, so we calculate the prop_diff with metadata=None.

To give the default value {} for metadata property.

This bug is similar with https://bugs.launchpad.net/heat/+bug/1635164.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/410066

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/410066
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=0fc8e6324c9fcc72b1438529dcb089806eb70d0d
Submitter: Jenkins
Branch: master

commit 0fc8e6324c9fcc72b1438529dcb089806eb70d0d
Author: huangtianhua <email address hidden>
Date: Tue Dec 13 15:25:42 2016 +0800

    Set default value for 'metadata' of nova server

    Set default value of 'metadata' to {}, to make sure
    update nova server success when observe_on_update
    is enabled.

    Change-Id: Iea29b9ce3bbf5dbf7ee33cdd9e2556305fa93ae3
    Closes-Bug: #1649222

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/heat 8.0.0.0b3 development milestone.