bin/haraka: also list installed NPM plugins

[msimerson]

When running haraka -l, also list NPM installed plugins.

related to haraka/haraka-plugin-access#25

[msimerson]

Sample output:

❯ ./bin/haraka -l
*global

plugins/
	avg
	backscatterer
	block_me
	bounce
	clamd
	data.signatures
	data.uribl
	delay_deny
	dkim_sign
	dkim_verify
	dns_list_base
	dnsbl
	dnswl
	early_talker
	esets
	graph
	greylist
	helo.checks
	mail_from.is_resolvable
	messagesniffer
	prevent_credential_leaks
	process_title
	profile
	rcpt_to.host_list_base
	rcpt_to.in_host_list
	rcpt_to.ldap
	rcpt_to.max_count
	record_envelope_addresses
	relay
	reseed_rng
	spamassassin
	status
	tarpit
	tls
	toobusy
	xclient

plugins/auth
	auth_base
	auth_bridge
	auth_ldap
	auth_proxy
	auth_vpopmaild
	flat_file

plugins/queue
	deliver
	discard
	lmtp
	qmail-queue
	quarantine
	rabbitmq
	rabbitmq_amqplib
	smtp_bridge
	smtp_forward
	smtp_proxy
	test

NPM packages (/Users/matt/git/haraka/Haraka)
	access
	aliases
	asn
	attachment
	auth-ldap
	dcc
	elasticsearch
	fcrdns
	geoip
	graph
	headers
	karma
	known-senders
	limit
	p0f
	qmail-deliverable
	rcpt-ldap
	recipient-routes
	redis
	rspamd
	spf
	uribl
	watch