Move Cluster.pm initialization code to a more obvious place

Commit 460c0076e8 added some module intialization code to set signal
handlers. However, that code has now become somewhat buried, as later
commits added new subroutines. Therefore, move the initialization code
to the module's INIT block where it won't become obscured.

src/test/perl/PostgreSQL/Test/Cluster.pm

@@ -175,6 +175,11 @@ INIT
 	$portdir =~ s!\\!/!g;
 	# Make sure the directory exists
 	mkpath($portdir) unless -d $portdir;
+
+	#
+	# Signal handlers
+	#
+	$SIG{TERM} = $SIG{INT} = sub { die "death by signal"; };
 }
 
 =pod
@@ -3350,13 +3355,6 @@ sub corrupt_page_checksum
 	return;
 }
 
-#
-# Signal handlers
-#
-$SIG{TERM} = $SIG{INT} = sub {
-	die "death by signal";
-};
-
 =pod
 
 =item $node->log_standby_snapshot(self, standby, slot_name)