Fix #746 (#769)

also fix broken text env

After the last couple of commits the tests ran correctly only on a
fresh db, in addition, the roles within the db were not created/dropped
on each request and we need that since their privileges differ and we
need to to have an absolute clean db on each execution

test/fixtures/roles.sql

@@ -0,0 +1,7 @@
+\set AUTHENTICATOR current_user
+DROP ROLE IF EXISTS postgrest_test_anonymous, postgrest_test_default_role, postgrest_test_author;
+CREATE ROLE postgrest_test_anonymous;
+CREATE ROLE postgrest_test_default_role;
+CREATE ROLE postgrest_test_author;
+
+GRANT postgrest_test_anonymous, postgrest_test_default_role, postgrest_test_author TO :USER;