Tolerate deleted trust on stack delete

Currently if a trust has already been deleted, the stack delete
fails and the stack becomes undeletable, so instead catch the
NotFound exception on trust delete, as there's nothing to do.

Change-Id: I1346cefdf6c5f2dea2bc9e2fdd4b9e7b14d60c31
Closes-Bug: #1266434
Update Loadbalancer default template to F20 image

Update the hard-coded default template for the LoadBalancer
resource, so it uses an image called F20-x86_64-cfntools

The Fedora cloud images now contain heat-cfntools, and I've
tested with Fedora-x86_64-20-20131211.1-sda.qcow2, downloaded
from http://fedoraproject.org/en/get-fedora#clouds and it works.

You can download this image direct to glance by doing:

glance image-create --name F20-x86_64-cfntools --disk-format qcow2 \
     --container-format bare --is-public true --copy-from \
     http://cloud.fedoraproject.org/fedora-20.x86_64.qcow2

For users of other distros, you can now override the default
template by copying the built-in template and specifying whatever
image or LB configuration you wish, see
https://review.openstack.org/#/c/64874/

Change-Id: I95e0451b03118a75be0a25f512304649eae42356
Closes-Bug: #1234375
Merge "Update Loadbalancer default template to F20 image"
Merge "Tolerate deleted trust on stack delete"