Refactor SnapshotProvider

lib/tfw/components/snapshot_provider.py

@@ -111,6 +111,12 @@ class SnapshotProvider:
         ))
         self._checkout(branch_name)
 
+    def _checkout(self, what):
+        self._run((
+            'git', 'checkout',
+            what
+        ))
+
     def restore_snapshot(self, date):
         commit = self._get_commit_from_timestamp(date)
         self._checkout(commit)
@@ -130,12 +136,6 @@ class SnapshotProvider:
             self.__last_valid_branch = self._branch
         return self.__last_valid_branch
 
-    def _checkout(self, what):
-        self._run((
-            'git', 'checkout',
-            what
-        ))
-
     @property
     def all_timelines(self):
         return self._branches