Move V2 sample files to respective directory

Some sample files like server, images etc are kept under api_samples/
directory.
As plan is to create clean directory structure for sample files for
V2, V2.1 and microversion, moving these sample files to respective directory
will help to achieve that.

Change-Id: I284d035f6fadb26a94bcb3586f4a8c72942ee423

nova/tests/functional/api_samples_test_base.py

@@ -32,6 +32,7 @@ class ApiSampleTestBase(integrated_helpers._IntegratedTestBase):
     ctype = 'json'
     all_extensions = False
     extension_name = None
+    sample_dir = None
     request_api_version = None
     _use_common_server_api_samples = False
 
@@ -54,8 +55,13 @@ class ApiSampleTestBase(integrated_helpers._IntegratedTestBase):
         if cls.all_extensions:
             parts.append('all_extensions')
         # Note(gmann): if _use_common_server_api_samples is set to True
-        # then common server sample files will be used.
-        if not cls._use_common_server_api_samples and cls.extension_name:
+        # then common server sample files present in 'servers' directory
+        # will be used.
+        elif cls._use_common_server_api_samples:
+            parts.append('servers')
+        elif cls.sample_dir:
+            parts.append(cls.sample_dir)
+        elif cls.extension_name:
             alias = importutils.import_class(cls.extension_name).alias
             parts.append(alias)
         parts.append(name + "." + cls.ctype + suffix)