Add some structure for backend abstraction

Add some backend placeholders.

implements blueprint backend-abstraction
Change-Id: Ia6bd3020d2f666ee317e1cf89ae2f3e10e6977aa

entropy/__main__.py

@@ -97,7 +97,8 @@ def start_engine(args):
     cfg = {
         args.name: {
             'cfg': os.path.join(os.getcwd(), args.engine_cfg),
-            'pid': os.getpid()
+            'pid': os.getpid(),
+            'backend': cfg_data['backend']
         }
     }
     utils.write_yaml(cfg, engine_cfg)

entropy/backends/__init__.py

@@ -0,0 +1,13 @@
+# Copyright (C) 2013 Yahoo! Inc. 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.

entropy/backends/db_backend.py

@@ -0,0 +1,13 @@
+# Copyright (C) 2013 Yahoo! Inc. 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.

entropy/backends/file_backend.py

@@ -0,0 +1,13 @@
+# Copyright (C) 2013 Yahoo! Inc. 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.