Refactors nova.image.glance unit tests for show()

This patches continues a patch series to cleanup and streamline the unit
tests for the nova.image.glance module. Here, we create true unit tests
for the GlanceImageService.show() method, stressing all code paths and
edges but only for that specific method, using mocks and no fake glance
image service.

This patch removes "unit" tests from the TestGlanceImageService that
called glance.GlanceImageService.show(), as those tests used the fake
glance service and the code paths are now more than covered by these new
mock-using tests.

Change-Id: I200a9e9812d6de011fa6faa8fb8dc570075ce902
Related-bug: #1293938
Refactors unit tests of image service detail()

We do not need to have "unit" tests that test the things like
pagination work with the glanceclient.images.detail() call. glanceclient
and glance have unit tests for that. What the unit tests for the glance
image service detail() method in Nova need is to test only the code
boundary that exists within the detail() method -- i.e. verify that the
calls to the glanceclient and other helper methods are made with the
right parameters.

This patch pulls the various unit tests out of the
TestGlanceImageService test class and into their own test class that
uses mocks and verifies each code path within the detail() method.

Next up is the create, update and delete methods of the
GlanceImageService class. The final piece is to rework the download unit
tests (which aren't unit tests but more functional tests that take
around a second each to run :(

Change-Id: I94897ff54a36a1af4258ba4a3c88b45c079f4bb5
Related-bug: #1293938
Make conductor expect ActionEventNotFound for action methods

The action_event_start() and action_event_finish() methods can
raise InstanceActionEventNotFound exceptions. Make sure these
get forwarded to the caller without logging them against the
conductor service.

Co-Authored-By: Matt Riedemann <mriedem@us.ibm.com>
Change-Id: I4d0bf185f515efac0eaa5245e5270e6e1877d8da
Merge "Refactors nova.image.glance unit tests for show()"
Merge "Refactors unit tests of image service detail()"