Comment 11 for bug 1712280

Reviewed: https://review.openstack.org/515454
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=31175a5641035abeec58c3f135ad09d3f231ac41
Submitter: Zuul
Branch: stable/pike

commit 31175a5641035abeec58c3f135ad09d3f231ac41
Author: Thomas Herve <email address hidden>
Date: Fri Sep 22 16:44:51 2017 +0200

    Defer exceptions in calculating node_data()

    When generating the node_data() for a resource, catch and store any
    exceptions (other than InvalidTemplateAttribute) encountered while
    getting attributes. Re-raise the exception at the point where we try to
    read the attribute value, including where we try to serialise the
    NodeData object to store in the database.

    In convergence, we generate and immediately serialise the NodeData, so
    this should result in no substantial change in behaviour there.

    In other situations (e.g. when we're just loading the data to show the
    stack), this prevents an error in attribute calculation from aborting
    the whole operation. The exception will still be raised if (and only if)
    the erroneous attribute is accessed, but may be handled more
    appropriately. For example, errors in calculating output values are
    handled by reporting an error only for that particular output.

    Change-Id: Idc97aee87405cc13e83be3373078b52e725850ea
    Co-Authored-By: Zane Bitter <email address hidden>
    Closes-Bug: #1712280
    (cherry picked from commit 4f4932c7900ae0e88e9a44f06b952c882474729e)