Set Stack id to None when deleted

If a Stack object has been removed from the database, we should reset its
ID to None so that if the object is used further, it will not be assumed
that it is represented in the database.

Change-Id: Iaa7e9327324f101487847362973bd7f8386ce44b
Fix error reporting in @stack_delete_after unit tests

If a unit test decorated with @stack_delete_after (to ensure that a stack
being tested is cleaned up) fails in such a way that the stack cannot be
cleaned up, the original error was suppressed, making debugging very
difficult. In this case, we should re-raise the original exception.

Change-Id: I2b0c326f819cd8a6bc772fe52deb14fb1c41bf93
heat tests : add parse_stack function to test utils

Add convenience function parse_stack to utils so it can be
reused in test to avoid duplication

Change-Id: I608e2227c695a9faecbd8ff78a1339b47174a006
heat tests : convert most tests to inline templates

Convert to inline minimal templates, to remove dependency on
in-tree templates which we plan to remove.  Note there are still
some more tests remaining which need similar changes (shardy todo)

Change-Id: I0864d1f15ea3b815d449277387440157f104bbf3
heat tests : separate Autoscaling and CW alarm tests

Currently the AutoScaling test also tests the CloudWatch Alarm
resource, so separate out the CW Alarm test to simplify things

Change-Id: Ia346ee49f3a363e2d63e801c74265545d7af1acf
Merge "heat tests : add parse_stack function to test utils"
Merge "heat tests : convert most tests to inline templates"
Merge "heat tests : separate Autoscaling and CW alarm tests"