Allow SFTPStorage to be configured via class variables

AUTHORS

@@ -42,6 +42,7 @@ By order of apparition, thanks:
     * Shaung Cheng (S3 docs)
     * Andrew Perry (Bug fixes in SFTPStorage)
     * Manuel Kaufmann (humitos)
+    * Jonathan Ehwald (Small tweak in SFTPStorage)
 
 
 Extra thanks to Marty for adding this in Django,

storages/backends/sftpstorage.py

@@ -27,29 +27,30 @@
 
 @deconstructible
 class SFTPStorage(Storage):
+    host = setting('SFTP_STORAGE_HOST')
+    params = setting('SFTP_STORAGE_PARAMS', {})
+    interactive = setting('SFTP_STORAGE_INTERACTIVE', False)
+    file_mode = setting('SFTP_STORAGE_FILE_MODE')
+    dir_mode = setting('SFTP_STORAGE_DIR_MODE')
+    uid = setting('SFTP_STORAGE_UID')
+    gid = setting('SFTP_STORAGE_GID')
+    known_host_file = setting('SFTP_KNOWN_HOST_FILE')
+    root_path = setting('SFTP_STORAGE_ROOT', '')
+    base_url = setting('MEDIA_URL')
 
     def __init__(self, host=None, params=None, interactive=None, file_mode=None,
                  dir_mode=None, uid=None, gid=None, known_host_file=None,
                  root_path=None, base_url=None):
-        self._host = host or setting('SFTP_STORAGE_HOST')
-
-        self._params = params or setting('SFTP_STORAGE_PARAMS', {})
-        self._interactive = setting('SFTP_STORAGE_INTERACTIVE', False) \
-            if interactive is None else interactive
-        self._file_mode = setting('SFTP_STORAGE_FILE_MODE') \
-            if file_mode is None else file_mode
-        self._dir_mode = setting('SFTP_STORAGE_DIR_MODE') if \
-            dir_mode is None else dir_mode
-
-        self._uid = setting('SFTP_STORAGE_UID') if uid is None else uid
-        self._gid = setting('SFTP_STORAGE_GID') if gid is None else gid
-        self._known_host_file = setting('SFTP_KNOWN_HOST_FILE') \
-            if known_host_file is None else known_host_file
-
-        self._root_path = setting('SFTP_STORAGE_ROOT', '') \
-            if root_path is None else root_path
-        self._base_url = setting('MEDIA_URL') if base_url is None else base_url
-
+        self._host = host or self.host
+        self._params = params or self.params
+        self._interactive = interactive or self.interactive
+        self._file_mode = file_mode or self.file_mode
+        self._dir_mode = dir_mode or self.dir_mode
+        self._uid = uid or self.uid
+        self._gid = gid or self.gid
+        self._known_host_file = known_host_file or self.known_host_file
+        self._root_path = root_path or self.root_path
+        self._base_url = base_url or self.base_url
         self._sftp = None
 
     def _connect(self):