Make the PlacementFixture usable without intercept

There are cases where it is necessary to use the PlacementFixture
without it running a wsgi-intercept, for example when you'd like
to run an indepdendent wsgi-intercept, as in the nova tests that
exercise the report client.

In the bug listed as partial below those report client tests were
using a nova conf global to initialize the wsgi intercept. They
just happened to be working because that CONF has the required
configuration settings. When placement's conf diverged [1] things
broke. A nova change which depends on this one will resolve the
bug.

Note that as a part of this change, the code which deletes
'sync_on_startup' (the new conf option) before configuring the
database, is adapted to be more flexible. There really is only
one conf setting that is required to start the placement database,
connection, and we'd like to make it possible for people to set
just that when doing tests or experiments and not have to worry
about extraneous optional things.

Some parameter descriptions are added to the PlacementFixture
__init__.

We should add more robust testing to all three of PlacementFixture,
fixtures.Database, and PlacementDirect, but at the moment we are
trying to fix a gate blocking bug.

Partial-Bug: #1818560

[1] Ie43a69be8b75250d9deca6a911eda7b722ef8648

Change-Id: I8c36f35dbe85b0c0db1a5b6b5389b160b68ca488

placement/db_api.py

@@ -23,7 +23,9 @@ placement_context_manager = enginefacade.transaction_context()
 def _get_db_conf(conf_group):
     conf_dict = dict(conf_group.items())
     # Remove the 'sync_on_startup' conf setting, enginefacade does not use it.
-    del conf_dict['sync_on_startup']
+    # Use pop since it might not be present in testing situations and we
+    # don't want to care here.
+    conf_dict.pop('sync_on_startup', None)
     return conf_dict
 
 

placement/tests/functional/fixtures/placement.py

@@ -30,6 +30,9 @@ class PlacementFixture(fixtures.Fixture):
     Runs a local WSGI server bound on a free port and having the Placement
     application with NoAuth middleware.
 
+    Optionally, the caller can choose to not use a wsgi-intercept and use
+    this fixture to set up configuration and (optionally) the database.
+
     It's possible to ask for a specific token when running the fixtures so
     all calls would be passing this token.
 
@@ -38,9 +41,21 @@ class PlacementFixture(fixtures.Fixture):
 
     Used by other services, including nova, for functional tests.
     """
-    def __init__(self, token='admin', conf_fixture=None, db=True):
+    def __init__(self, token='admin', conf_fixture=None, db=True,
+                 use_intercept=True):
+        """Create a Placement Fixture.
+
+        :param token: The value to be used when passing an auth token
+                      header in HTTP requests.
+        :param conf_fixture: An oslo_conf.fixture.Config. If provided, config
+                             will be based from it.
+        :param db: Whether to start the Database fixture.
+        :param use_intercept: If true, install a wsgi-intercept of the
+                              placement WSGI app.
+        """
         self.token = token
         self.db = db
+        self.use_intercept = use_intercept
         self.conf_fixture = conf_fixture
 
     def setUp(self):
@@ -60,6 +75,7 @@ class PlacementFixture(fixtures.Fixture):
 
         self.useFixture(policy_fixture.PolicyFixture(self.conf_fixture))
 
+        if self.use_intercept:
             loader = deploy.loadapp(self.conf_fixture.conf)
             app = lambda: loader
             self.endpoint = 'http://%s/placement' % uuidutils.generate_uuid()