Catch error deleting trust on stack delete

When deleting a stack, it's possible for deleting the trust to fail,
for example if the user deleting the stack is not the user who created
it, or an admin (which raises a Forbidden error), or due to some
other transient error e.g connection to keystone interrupted.

Currently in this case, we fail to mark the stack deleted in the DB
and leave the status "DELETE, COMPLETE", which is misleading.

Change-Id: Ie8e9ea48bc4f44e56ff4764123fcca733f5bd458
Partial-Bug: #1247200
Ensure that members is a list

self.properties.get('members') should not be None.  Ensure that
an empty list is returned instead.

Change-Id: I01d191eafebac30ad25505b312ff6e936181bdbf
Closes-Bug: #1255697
Imported Translations from Transifex

Change-Id: Iae4d296728f802cc217d36f12f296cbaa75055c7
Merge "Ensure that members is a list"
Merge "Imported Translations from Transifex"
Merge "Catch error deleting trust on stack delete"