Ban db import from nova/virt

This makes hacking.py complain if someone adds something like:

  from nova import db

into any of the files in nova/virt/* (aside from the fake.py file).
It also removes the rest of the dangling db imports that are no
longer needed.

Yay!

Change-Id: Iba3d53b87e65e33a55f8e5033b5d1d33b28d12f7

HACKING.rst

@@ -33,6 +33,7 @@ Imports
 - Do not import objects, only modules (*)
 - Do not import more than one module per line (*)
 - Do not make relative imports
+- Do not make new nova.db imports in nova/virt/*
 - Order your imports by the full module path
 - Organize your imports according to the following template
 

nova/virt/hyperv/vmops.py

@@ -22,7 +22,6 @@ import os
 import uuid
 
 from nova import config
-from nova import db
 from nova import exception
 from nova import flags
 from nova.openstack.common import cfg

nova/virt/virtapi.py

@@ -15,9 +15,6 @@
 #    under the License.
 
 
-from nova import db
-
-
 class VirtAPI(object):
     def instance_update(self, context, instance_uuid, updates):
         """Perform an instance update operation on behalf of a virt driver

nova/virt/xenapi/driver.py

@@ -48,7 +48,6 @@ from eventlet import timeout
 
 from nova import config
 from nova import context
-from nova import db
 from nova import exception
 from nova import flags
 from nova.openstack.common import cfg

nova/virt/xenapi/host.py

@@ -24,7 +24,6 @@ import logging
 from nova.compute import task_states
 from nova.compute import vm_states
 from nova import context
-from nova import db
 from nova import exception
 from nova import notifications
 from nova.openstack.common import jsonutils

nova/virt/xenapi/pool.py

@@ -23,7 +23,6 @@ import urlparse
 
 from nova.compute import rpcapi as compute_rpcapi
 from nova import config
-from nova import db
 from nova import exception
 from nova import flags
 from nova.openstack.common import cfg

tools/hacking.py

@@ -271,6 +271,13 @@ def nova_import_alphabetical(logical_line, line_number, lines):
                 % (split_previous[1], split_line[1]))
 
 
+def nova_import_no_db_in_virt(logical_line, filename):
+    if ("nova/virt" in filename and
+        not filename.endswith("fake.py") and
+        "nova import db" in logical_line):
+        yield (0, "NOVA N307: nova.db import not allowed in nova/virt/*")
+
+
 def nova_docstring_start_space(physical_line):
     """Check for docstring not start with space.