Error messages from nested stacks are awful

[Zane Bitter]

Since the shift to handling nested stacks over RPC, error messages from within them have become utterly incomprehensible. The nested stack resource reports its status as:

ResourceUnknownStatus: Resource failed - Unknown status FAILED due to "..."

Which is ridiculous. The status isn't unknown, we should know exactly what FAILED means and just pass the error message along. A couple of layers of nested stacks deep (not uncommon) and we are quickly into absurdities the likes of which were previously restricted to such things as C++ linker errors:

ResourceUnknownStatus: Resource failed - Unknown status FAILED due to "Resource CREATE failed: ResourceUnknownStatus: Resource failed - Unknown status FAILED due to "Resource CREATE failed: Error: Deployment to server failed: deploy_status_code : Deployment exited with non-zero status code: 6""

It doesn't even add any useful information, like the name of the resource that failed, just noise.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/188228

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/kilo
Review: https://review.openstack.org/195854

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/195854
Committed: https://git.openstack.org/cgit/openstack/heat/commit/?id=ed52c86549e65544ca9813d0da135b29d31a4460
Submitter: Jenkins
Branch: stable/kilo

commit ed52c86549e65544ca9813d0da135b29d31a4460
Author: Angus Salkeld <email address hidden>
Date: Wed Jun 24 08:52:08 2015 +1000

    Produce more meaningful exception messages in nested stacks

    This produces a nested exception like:
     'ValueError: resources.nested.resources.my_server: it is broken, sorry'

    This re-uses the path mechanism that StackValidationFailed exception
    uses.

    Cherry-picked from caa1bd860233296fa3dbf8197667f38c10719611
    Change-Id: Id5204c15ee96784e04522ab3c5a8e66900f9a1d3
    Closes-bug: 1459837