Use test functions in pg_rewind test module

Commit 61081e7 introduced pg_rewind along with the test suite, which
ensured that subroutines didn't incur more than one test to plan.  Now
that we no longer explicitly plan tests (since 549ec20),  we can use
the usual Test::More functions.

Reviewed-by: Andrew Dunstan <andrew@dunslane.net>
Discussion: https://postgr.es/m/AA527525-F0CC-4AA2-AF98-543CABFDAF59@yesql.se

Author: danielgustafsson

src/bin/pg_rewind/t/RewindTest.pm

@@ -102,21 +102,10 @@ sub check_query
 	  ],
 	  '>', \$stdout, '2>', \$stderr;
 
-	# We don't use ok() for the exit code and stderr, because we want this
-	# check to be just a single test.
-	if (!$result)
-	{
-		fail("$test_name: psql exit code");
-	}
-	elsif ($stderr ne '')
-	{
-		diag $stderr;
-		fail("$test_name: psql no stderr");
-	}
-	else
-	{
-		is($stdout, $expected_stdout, "$test_name: query result matches");
-	}
+	is($result, 1, "$test_name: psql exit code");
+	is($stderr, '', "$test_name: psql no stderr");
+	is($stdout, $expected_stdout, "$test_name: query result matches");
+
 	return;
 }