Fix gabbi tests

When the tests have been migrated to this repository, the gabbi test
generates have never raise error...

This change fixes that.

It also fixes tests that doesn't pass anymore.
It removes useless stack downscaling,  because it takes too many times
for no additional value (alarm update/metric update are tested by other
tests).

Change-Id: I09cd0569f90e873cf4b7f05ec9c14496c9551fcc
8 files changed