Adding description for testcases - compute part11

When Tempest is used in customer site, often we are required to
provide a testcase list including testcase names and descriptions.
Now no this kind of doc is available, so we can add descriptions
with the format of doc string for every testcase, so later we
can generata such a testcase description list.

There are hundreds of testcases missing descriptions, so we can
add them gradually, and limit the modified files in one patch
for the convenience of reviewing.

Change-Id: I5bf95ca579b731ca4baefb590edb8e265126ce4f
partially-implements: blueprint testcase-description
diff --git a/tempest/api/compute/admin/test_server_diagnostics.py b/tempest/api/compute/admin/test_server_diagnostics.py
index 005efdd..d855a62 100644
--- a/tempest/api/compute/admin/test_server_diagnostics.py
+++ b/tempest/api/compute/admin/test_server_diagnostics.py
@@ -19,6 +19,8 @@
 
 
 class ServerDiagnosticsTest(base.BaseV2ComputeAdminTest):
+    """Test server diagnostics with compute microversion less than 2.48"""
+
     min_microversion = None
     max_microversion = '2.47'
 
@@ -29,6 +31,7 @@
 
     @decorators.idempotent_id('31ff3486-b8a0-4f56-a6c0-aab460531db3')
     def test_get_server_diagnostics(self):
+        """Test getting server diagnostics"""
         server_id = self.create_test_server(wait_until='ACTIVE')['id']
         diagnostics = self.client.show_server_diagnostics(server_id)
 
@@ -41,6 +44,8 @@
 
 
 class ServerDiagnosticsV248Test(base.BaseV2ComputeAdminTest):
+    """Test server diagnostics with compute microversion greater than 2.47"""
+
     min_microversion = '2.48'
     max_microversion = 'latest'
 
@@ -51,6 +56,7 @@
 
     @decorators.idempotent_id('64d0d48c-dff1-11e6-bf01-fe55135034f3')
     def test_get_server_diagnostics(self):
+        """Test getting server diagnostics"""
         server_id = self.create_test_server(wait_until='ACTIVE')['id']
         # Response status and filed types will be checked by json schema
         self.client.show_server_diagnostics(server_id)