heat engine : ensure create thread exits on stack delete

Detect GreenletExit exception when creating resources - this may
happen if the stack gets deleted while the stack is still in
CREATE_IN_PROGRESS state.  If we don't detect this then the stack
continues trying to create resources during/after the stack has been
deleted, with predictably nasty results..

fixes bug 1096150

Change-Id: Ieb6ed38d0000cd6fe3bc1af2eb5d2e5eecc74fb4
Signed-off-by: Steven Hardy <shardy@redhat.com>
heat engine : allow NestedStack template validation to work

Nested stack templates (e.g WordPress_Composed_Instances.template)
will currently fail validation because FnGetAtt attempts to get
outputs for a stack which doesn't yet exist.  So add a fallback which
returns a string "None" for Outputs.* which will allow template
validation to succeed, and will still return the actual output when
the nested stack has actually been created.

fixes bug 1097290

Change-Id: Ic3f48cfc2f047c104946d6dde533143d0d91a32c
Signed-off-by: Steven Hardy <shardy@redhat.com>
heat engine : DBInstance fix so nested stack is deleted

Currently the RDS DBInstance resource inherits from stack.Stack but it
should be stack.NestedStack, which implements handle_delete whereas
stack.Stack does not, meaning the DBInstance nested stack is never
deleted when the owning stack gets deleted.

fixes bug 1097299

Change-Id: I865611d4de9ea4c3caa43c7a11a28924602a5b0d
Signed-off-by: Steven Hardy <shardy@redhat.com>
Merge "heat engine : ensure create thread exits on stack delete"
Merge "heat engine : allow NestedStack template validation to work"