Apply a show_image rule of GET to clients

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

Partially implements blueprint consistent-service-method-names

Change-Id: I08a0a0e9f11fa6c225404cac63c0541dd345e77c
diff --git a/tempest/api/image/v1/test_images.py b/tempest/api/image/v1/test_images.py
index fc75d95..6c25c93 100644
--- a/tempest/api/image/v1/test_images.py
+++ b/tempest/api/image/v1/test_images.py
@@ -77,7 +77,7 @@
         self.assertEqual('New Http Image', body.get('name'))
         self.assertFalse(body.get('is_public'))
         self.client.wait_for_image_status(image_id, 'active')
-        self.client.get_image(image_id)
+        self.client.show_image(image_id)
 
     @test.idempotent_id('05b19d55-140c-40d0-b36b-fafd774d421b')
     def test_register_image_with_min_ram(self):