Add some more pg_receivewal tests

Add some more tests for the --create-slot and --drop-slot options,
verifying that the right kind of slot was created and that the slot was
dropped.  While working on an unrelated patch for pg_basebackup, some of
this was temporarily broken without any tests noticing.

src/bin/pg_basebackup/t/020_pg_receivewal.pl

@@ -2,7 +2,7 @@ use strict;
 use warnings;
 use TestLib;
 use PostgresNode;
-use Test::More tests => 14;
+use Test::More tests => 17;
 
 program_help_ok('pg_receivewal');
 program_version_ok('pg_receivewal');
@@ -30,8 +30,12 @@ my $slot_name = 'test';
 $primary->command_ok(
 	[ 'pg_receivewal', '--slot', $slot_name, '--create-slot' ],
 	'creating a replication slot');
+my $slot = $primary->slot($slot_name);
+is($slot->{'slot_type'}, 'physical', 'physical replication slot was created');
+is($slot->{'restart_lsn'}, '', 'restart LSN of new slot is null');
 $primary->command_ok([ 'pg_receivewal', '--slot', $slot_name, '--drop-slot' ],
 	'dropping a replication slot');
+is($primary->slot($slot_name)->{'slot_type'}, '', 'replication slot was removed');
 
 # Generate some WAL.  Use --synchronous at the same time to add more
 # code coverage.  Switch to the next segment first so that subsequent