Ignore sqla-migrate inspect.getargspec deprecation warnings

This adds a warnings filter to ignore the "inspect.getargspec"
warnings from sqlalchemy-migrate until bug 1814288 is fixed
in that library.

Change-Id: Id8c02e745742980d3dd0a24e6e2b7a5859f3cb88
Related-Bug: #1813147

nova/tests/fixtures.py

@@ -849,6 +849,13 @@ class WarningsFixture(fixtures.Fixture):
             'ignore', message=".* 'VIFPortProfileOVSRepresentor' .* "
             "is deprecated", category=PendingDeprecationWarning)
 
+        # TODO(mriedem): Change (or remove) this DeprecationWarning once
+        # https://bugs.launchpad.net/sqlalchemy-migrate/+bug/1814288 is fixed.
+        warnings.filterwarnings(
+            'ignore', message='inspect\.getargspec\(\) is deprecated',
+            category=DeprecationWarning,
+            module='migrate.versioning.script.py')
+
         self.addCleanup(warnings.resetwarnings)