Minor fixes. Raise exception when method is not implemented

Change-Id: I0080263c36959f24311c474d7241108f8c24bd48
Signed-off-by: tierno <alfonso.tiernosepulveda@telefonica.com>
diff --git a/osm_common/fsbase.py b/osm_common/fsbase.py
index 60c0c0f..e975409 100644
--- a/osm_common/fsbase.py
+++ b/osm_common/fsbase.py
@@ -24,19 +24,19 @@
         pass
 
     def mkdir(self, folder):
-        pass
+        raise FsException("Method 'mkdir' not implemented")
 
     def file_exists(self, storage):
-        pass
+        raise FsException("Method 'file_exists' not implemented")
 
     def file_size(self, storage):
-        pass
+        raise FsException("Method 'file_size' not implemented")
 
     def file_extract(self, tar_object, path):
-        pass
+        raise FsException("Method 'file_extract' not implemented")
 
     def file_open(self, storage, mode):
-        pass
+        raise FsException("Method 'file_open' not implemented")
 
     def file_delete(self, storage, ignore_non_exist=False):
-        pass
+        raise FsException("Method 'file_delete' not implemented")