Rehome unit tests to `tests\unit` folder

Currently only unit tests are executed, but other type could be needed
(functional, for example). All tests in ``os_vif``, ``vif_plug_ovs`` and
``vif_plug_linux_bridge`` are moved to ``tests\unit`` folder.

TrivialFix

Change-Id: I3ea64a407b5fa8b23e0c8e656a55524139d1b79f

os_vif/tests/unit/test_exception.py

@@ -13,7 +13,7 @@
 import six
 
 from os_vif import exception
-from os_vif.tests import base
+from os_vif.tests.unit import base
 
 """Mostly inspired by os-brick's tests."""
 

os_vif/tests/unit/test_host_info.py

@@ -12,7 +12,7 @@
 
 from os_vif import exception
 from os_vif import objects
-from os_vif.tests import base
+from os_vif.tests.unit import base
 
 
 class TestHostInfo(base.TestCase):

os_vif/tests/unit/test_os_vif.py

@@ -18,7 +18,7 @@ import os_vif
 from os_vif import exception
 from os_vif import objects
 from os_vif import plugin
-from os_vif.tests import base
+from os_vif.tests.unit import base
 
 
 class DemoPlugin(plugin.PluginBase):

os_vif/tests/unit/test_vif.py

@@ -15,7 +15,7 @@ from oslo_versionedobjects import fixture
 
 import os_vif
 from os_vif import objects
-from os_vif.tests import base
+from os_vif.tests.unit import base
 
 
 class TestVIFS(base.TestCase):