Make specifying zookeeper in topo files optional

[lukedirtwalker]

For pure golang topologies we don't require zookeeper anymore,
so we should also not require zookeeper to be specified in the topo file.

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This change is 

[worxli]

Reviewed 2 of 3 files at r1.
Reviewable status: 2 of 3 files reviewed, 1 unresolved discussion (waiting on @lukedirtwalker and @worxli)

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topology/Tiny.topo, line 3 at r1 (raw file):

--- # Tiny Topology
defaults:
  zookeepers:

why do you only remove it in Tiny?

[lukedirtwalker]

Reviewable status: 2 of 3 files reviewed, 1 unresolved discussion (waiting on @worxli)

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topology/Tiny.topo, line 3 at r1 (raw file):

Previously, worxli (Lukas Bischofberger) wrote…

why do you only remove it in Tiny?

so that we still see how it looks like :D

[lukedirtwalker]

Reviewable status: 2 of 3 files reviewed, 1 unresolved discussion (waiting on @worxli)

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topology/Tiny.topo, line 3 at r1 (raw file):

Previously, lukedirtwalker (Lukas Vogel) wrote…

so that we still see how it looks like :D

Done.

[worxli]

Reviewed 1 of 3 files at r1, 2 of 2 files at r2, 3 of 3 files at r3.
Reviewable status: complete! all files reviewed, all discussions resolved

[worxli]

Reviewed 1 of 1 files at r4.
Reviewable status: complete! all files reviewed, all discussions resolved