Refactor Vault a bit, mainly pytest, config and BaseDb-based VaultBackend

• Extract the main cli command in a dedicated cli.py module and make it an entrypoint

• Refactor the VaultBackend to use BaseDb and pool-based db access

• Normalize the configuration of VaultBackend and cooker

  ensure every service for which an (remote or local) access is needed uses the same config structure (dict with 'cls' and 'args' keys).

• Rewrite tests using pytest's fuxture and adapt them to recent refactorings

---

Migrated from D1108 (view on Phabricator)

swh/vault/api/server.py

@@ -193,13 +193,8 @@ def make_app(config, **kwargs):
     return app
 
 
-api_cfg = None
-
-
 def make_app_from_configfile(config_path=DEFAULT_CONFIG_PATH, **kwargs):
-    global api_cfg
-    if not api_cfg:
-        api_cfg = config.read(config_path, DEFAULT_CONFIG)
+    api_cfg = config.read(config_path, DEFAULT_CONFIG)
     return make_app(api_cfg, **kwargs)