Add error pattern checks for some TAP tests for non-existing objects

Some tests are updated to use command_fails_like(), gaining a check for
the error output generated.  The test changed in pg_amcheck has come up
after noticing that an incorrect option name still made the test to
pass, while the command failed.  The three other tests changed in
src/bin/scripts/ have been noticed by me, in passing.

Author: Dagfinn Ilmari Mannsåker, Michael Paquier
Discussion: https://postgr.es/m/87bjvy50cs.fsf@wibble.ilmari.org

src/bin/pg_amcheck/t/002_nonesuch.pl

@@ -85,7 +85,10 @@ $node->command_checks_all(
 # Failing to connect to the initial database due to bad username is an error.
 $node->command_checks_all(
 	[ 'pg_amcheck', '--username' => 'no_such_user', 'postgres' ],
-	1, [qr/^$/], [], 'checking with a non-existent user');
+	1,
+	[qr/^$/],
+	[qr/role "no_such_user" does not exist/],
+	'checking with a non-existent user');
 
 #########################################
 # Test checking databases without amcheck installed

src/bin/scripts/t/010_clusterdb.pl

@@ -21,7 +21,9 @@ $node->issues_sql_like(
 	qr/statement: CLUSTER;/,
 	'SQL CLUSTER run');
 
-$node->command_fails([ 'clusterdb', '--table' => 'nonexistent' ],
+$node->command_fails_like(
+	[ 'clusterdb', '--table' => 'nonexistent' ],
+	qr/relation "nonexistent" does not exist/,
 	'fails with nonexistent table');
 
 $node->safe_psql('postgres',

src/bin/scripts/t/050_dropdb.pl

@@ -28,7 +28,9 @@ $node->issues_sql_like(
 	qr/statement: DROP DATABASE foobar2 WITH \(FORCE\);/,
 	'SQL DROP DATABASE (FORCE) run');
 
-$node->command_fails([ 'dropdb', 'nonexistent' ],
+$node->command_fails_like(
+	[ 'dropdb', 'nonexistent' ],
+	qr/database "nonexistent" does not exist/,
 	'fails with nonexistent database');
 
 # check that invalid database can be dropped with dropdb

src/bin/scripts/t/070_dropuser.pl

@@ -22,7 +22,9 @@ $node->issues_sql_like(
 	qr/statement: DROP ROLE regress_foobar1/,
 	'SQL DROP ROLE run');
 
-$node->command_fails([ 'dropuser', 'regress_nonexistent' ],
+$node->command_fails_like(
+	[ 'dropuser', 'regress_nonexistent' ],
+	qr/role "regress_nonexistent" does not exist/,
 	'fails with nonexistent user');
 
 done_testing();