Pop name from volume.base.create_server

In volume.base.create_server, name argument should be popped out from
kwargs, otherwise the call to create_server(name='xxx') will raise
"TypeError: create_test_server() got multiple values for keyword
argument 'name'"

Change-Id: I837443a2c028692db512a017aed11d3dad21c799
diff --git a/tempest/api/volume/base.py b/tempest/api/volume/base.py
index b788d54..bc2c0ae 100644
--- a/tempest/api/volume/base.py
+++ b/tempest/api/volume/base.py
@@ -173,7 +173,7 @@
                 pass
 
     def create_server(self, **kwargs):
-        name = kwargs.get(
+        name = kwargs.pop(
             'name',
             data_utils.rand_name(self.__class__.__name__ + '-instance'))