Converted blueprint to us flyweight pattern

This change converts the blueprint hook to use the flyweight pattern to
only create one instance of the blueprint per environment. This
facilitates the genesis v3.1.0 release, which allows hooks to run only
once and cache the results for the duration of the genesis run, reducing
the time it takes to run genesis.

Also fixes missing os-conf.yml override in blueprint (that isn't being
used yet due to a bug in genesis v3.0.x releases).

hooks/blueprint.pm

@@ -13,18 +13,27 @@ use parent qw(Genesis::Hook::Blueprint);
 
 use Genesis qw/bail info warning error in_array new_enough/;
 
+my %blueprint_for_env = ();
 sub init {
 	my $class = shift;
+
+	# Flyweight pattern: only create one instance of the blueprint per environment
+	my @args = @_;
+	if ({@_}->{env}) {
+		my $env_name = {@_}->{env}->name;;
+		return $blueprint_for_env{$env_name} if $blueprint_for_env{$env_name};
+	}
+
 	my $obj = $class->SUPER::init(@_);
 	$obj->{features} = [$obj->env->features];
-	$obj->{files} = [];
 	$obj->check_minimum_genesis_version('3.0.0-rc.1');
-	return $obj;
+	return $blueprint_for_env{$obj->env->name} = $obj;
 }
 
 sub perform {
 	my ($blueprint) = @_; # $blueprint is '$self'
 
+	$blueprint->{files} = [];
 	$blueprint->{ocfp_env_type} = '';
 	if ($blueprint->want_feature('ocfp')) {
 		$blueprint->{ocfp_env_type} = ($blueprint->env->name =~ /.*-mgmt.*/)
@@ -220,6 +229,7 @@ sub perform {
 	$blueprint->add_files(qw(
 		bosh-deployment/jumpbox-user.yml
 		overlay/addons/op-users.yml
+		overlay/releases/os-conf.yml
 	)) unless $blueprint->want_feature('skip-op-users');
 
 	for my $feature ($blueprint->features) {