Implements test_(create|update)_metadata_key_error

Implements function for both create and update passing
a blank key to force an error.

Partially implements bp missing-tempest-tests

Change-Id: I3dd7e4a876d74d5b481356afc8ba4c8976cc4090
diff --git a/tempest/tests/compute/servers/test_server_metadata.py b/tempest/tests/compute/servers/test_server_metadata.py
index 7db963e..1fe5bb3 100644
--- a/tempest/tests/compute/servers/test_server_metadata.py
+++ b/tempest/tests/compute/servers/test_server_metadata.py
@@ -87,6 +87,16 @@
 
         # no teardown - all creates should fail
 
+    @attr(type='negative')
+    def test_create_metadata_key_error(self):
+        # Blank key should trigger an error.
+        meta = {'': 'data1'}
+        name = rand_name('server')
+        self.assertRaises(exceptions.BadRequest,
+                          self.create_server_with_extras,
+                          name, self.image_ref,
+                          self.flavor_ref, meta=meta)
+
     def test_update_server_metadata(self):
         # The server's metadata values should be updated to the
         # provided values
@@ -177,6 +187,14 @@
             self.fail('An update should not happen for a nonexistant image')
 
     @attr(type='negative')
+    def test_update_metadata_key_error(self):
+        # Blank key should trigger an error.
+        meta = {'': 'data1'}
+        self.assertRaises(exceptions.BadRequest,
+                          self.client.update_server_metadata,
+                          self.server_id, meta=meta)
+
+    @attr(type='negative')
     def test_delete_nonexistant_server_metadata_item(self):
         # Negative test: Should not be able to delete metadata item from a
         # nonexistant server