S3, Glacier, WebDAV: Fix bug that prevented accessing the creds when the repository was configured with encryption=shared embedcreds=yes.

Since encryption=shared, the encryption key is stored in the git repo, so
there is no point at all in encrypting the creds, also stored in the git
repo with that key. So `initremote` doesn't. The creds are simply stored
base-64 encoded.

However, it then tried to always decrypt creds when encryption was used..

Remote/Helper/Encryptable.hs

@@ -71,18 +71,21 @@ encryptionSetup c = maybe genCipher updateCipher $ extractCipher c
 {- Gets encryption Cipher. The decrypted Ciphers are cached in the Annex
  - state. -}
 remoteCipher :: RemoteConfig -> Annex (Maybe Cipher)
-remoteCipher c = go $ extractCipher c
+remoteCipher = fmap fst <$$> remoteCipher'
+
+remoteCipher' :: RemoteConfig -> Annex (Maybe (Cipher, StorableCipher))
+remoteCipher' c = go $ extractCipher c
   where
 	go Nothing = return Nothing
 	go (Just encipher) = do
 		cache <- Annex.getState Annex.ciphers
 		case M.lookup encipher cache of
-			Just cipher -> return $ Just cipher
+			Just cipher -> return $ Just (cipher, encipher)
 			Nothing -> do
 				showNote "gpg"
 				cipher <- liftIO $ decryptCipher encipher
 				Annex.changeState (\s -> s { Annex.ciphers = M.insert encipher cipher cache })
-				return $ Just cipher
+				return $ Just (cipher, encipher)
 
 {- Checks if the remote's config allows storing creds in the remote's config.
  -