Added Trove (database) version API tests

Added a new file "test_versions.py" to verify the current
version of the Database API.  Required supporting
functions are added in a new client file "versions_client.py"
under the JSON interface.
Modified api/base.py, etc/tempest.conf.sample, clients.py and
config.py files

Partially implements blueprint: trove-tempest

Change-Id: I3dbe4e40b8b2a1ec3c69573dd40c3c8a643d73d6
diff --git a/tempest/services/database/json/versions_client.py b/tempest/services/database/json/versions_client.py
new file mode 100644
index 0000000..0269c43
--- /dev/null
+++ b/tempest/services/database/json/versions_client.py
@@ -0,0 +1,38 @@
+# Copyright 2014 OpenStack Foundation
+# All Rights Reserved.
+#
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import urllib
+
+from tempest.common import rest_client
+from tempest import config
+
+CONF = config.CONF
+
+
+class DatabaseVersionsClientJSON(rest_client.RestClient):
+
+    def __init__(self, auth_provider):
+        super(DatabaseVersionsClientJSON, self).__init__(auth_provider)
+        self.skip_path()
+        self.service = CONF.database.catalog_type
+
+    def list_db_versions(self, params=None):
+        """List all versions."""
+        url = ''
+        if params:
+            url += '?%s' % urllib.urlencode(params)
+
+        resp, body = self.get(url)
+        return resp, self._parse_resp(body)