Fix log capturing fixture

Instead of nuking the unit test logs capture them according
to how tempest (and oslotest) capture them so that the tests
when ran locally provide the full logging output instead of
a miniaturized version.

This adds in the following environment variables which can
be used to control testr captured logging:

- OS_LOG_CAPTURE (turns on log capturing so that the testr
  repository will have log output, at a INFO level)
- OS_DEBUG (changes the captured logging level from INFO
  to DEBUG, only useful when OS_LOG_CAPTURE is enabled)

It also creates a lambda that is used to test whether an
environment is enabled (avoiding recreating the same set
of checks in multiple places).

Change-Id: I63d9a1b7fc6e7591fd6309cf68d9269117c023a6
Add task/flow listener support around the volume api flow

This will add in logging of what is occurring around the
actions taken by taskflow when taskflow executes the initial
create_volume workflow.

Since the oslo logging module will include the request_id of
the currently active request (per greenthread) this will make
it easier to understand and debug the actions occurring inside
taskflow's engine concept.

Part of blueprint task-logging

Change-Id: I57a6f85ecac37fc4f97033eb3b7a0dc8bd35a886
Merge "Fix log capturing fixture"
Merge "Add task/flow listener support around the volume api flow"