Make migrations (mostly) idempotent.

config/sql/nonces.sql

@@ -2,20 +2,20 @@
 
 -- DROP TABLE public.nonces;
 
-CREATE TABLE public.nonces
+CREATE TABLE IF NOT EXISTS public.nonces
 (
   nonce text,
   expire timestamp with time zone,
   CONSTRAINT nonces_id_key UNIQUE (nonce)
 );
 
-GRANT ALL ON TABLE public.nonces TO kemal;
+GRANT ALL ON TABLE public.nonces TO current_user;
 
 -- Index: public.nonces_nonce_idx
 
 -- DROP INDEX public.nonces_nonce_idx;
 
-CREATE INDEX nonces_nonce_idx
+CREATE INDEX IF NOT EXISTS nonces_nonce_idx
   ON public.nonces
   USING btree
   (nonce COLLATE pg_catalog."default");