2a0f06147e
stestr can leave a .stestr directory from which subunit cannot be generated after an initial run that fails due to a python import/parse error. In order to determine if a run will be able to generate subunit output, check for the '.stestr/failing' file. NOTE: This is **NOT** an indication of a failing run. It's a file that will be present in the .stestr directory if an entire run has happened and acts as a marker that the directory has enough information to export a subunit stream. Change-Id: Id1dd696c81da09e9d2e5fe350337b73eb0646d2d