Fix tests for fixtures 4.0.0

This fixes ForeignKeyConstraintFixture for the db
tests. Also drops install_command from tox.ini.

Change-Id: I3d0abf68cae89566f4d346cd16919a6050168130

heat/tests/utils.py

@@ -220,15 +220,19 @@ class JsonRepr(object):
 
 
 class ForeignKeyConstraintFixture(fixtures.Fixture):
-    def __init__(self, sqlite_fk=True):
-        self.enable_fkc = sqlite_fk
+
+    def __init__(self):
+        self.engine = get_engine()
 
     def _setUp(self):
-        new_context = db_api.db_context.make_new_manager()
-        new_context.configure(sqlite_fk=self.enable_fkc)
+        if self.engine.name == 'sqlite':
+            self.engine.execute("PRAGMA foreign_keys=ON")
 
-        self.useFixture(fixtures.MockPatchObject(db_api, '_facade', None))
-        self.addCleanup(db_api.db_context.patch_factory(new_context._factory))
+            def disable_fks():
+                with self.engine.connect() as conn:
+                    conn.connection.rollback()
+                    conn.execute("PRAGMA foreign_keys=OFF")
+            self.addCleanup(disable_fks)
 
 
 class AnyInstance(object):

tox.ini

@@ -9,7 +9,6 @@ basepython = python3
 setenv = VIRTUAL_ENV={envdir}
          PYTHONWARNINGS=default::DeprecationWarning
          OS_TEST_PATH=heat/tests
-install_command = pip install -c{env:UPPER_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master} {opts} {packages}
 usedevelop = True
 deps = -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
        -r{toxinidir}/requirements.txt
@@ -59,6 +58,7 @@ allowlist_externals =
   rm
 deps =
   -c{env:TOX_CONSTRAINTS_FILE:https://releases.openstack.org/constraints/upper/master}
+  -r{toxinidir}/requirements.txt
   -r{toxinidir}/doc/requirements.txt
 commands =
   rm -rf doc/build