Apply other "get" rule of GET to image v2 client

[GET /resources] methods should be "list_<resource name>s" or
"show_<resource name>", so this patch applies the part of the
rule to image client.

NOTE: This patch renames get_image_file to load_image_file
because the method gets the content of file. So show_image_file
didn't fit to its meaning. In addition, this renames store_image
to store_image_file for consistency.

Partially implements blueprint consistent-service-method-names

Change-Id: I2b354ff7192bea20339c61bedcd2f11eee455381
diff --git a/tempest/api/telemetry/test_telemetry_notification_api.py b/tempest/api/telemetry/test_telemetry_notification_api.py
index 73a5fd4..d49b2ba 100644
--- a/tempest/api/telemetry/test_telemetry_notification_api.py
+++ b/tempest/api/telemetry/test_telemetry_notification_api.py
@@ -67,8 +67,8 @@
     def test_check_glance_v2_notifications(self):
         body = self.create_image(self.image_client_v2)
 
-        self.image_client_v2.store_image(body['id'], "file")
-        self.image_client_v2.get_image_file(body['id'])
+        self.image_client_v2.store_image_file(body['id'], "file")
+        self.image_client_v2.load_image_file(body['id'])
 
         query = 'resource', 'eq', body['id']