Zk should be default

[vogievetsky]

Fixing a bug introduced in #13550 where the change makes it that there is no ZK by default.

[kfaraz]

Don't these lines already handle this? (zk = True)

druid/examples/bin/start-druid-main.py

Lines 238 to 241 in 7682b0b

	if len(service_list) == 0:
	# start all services
	service_list = DEFAULT_SERVICES
	zk = True

[findingrish]

ZK is not needed in here.
It is passed around as a flag internally.