cluster: remove hooks

[oleg-jukovec]

Please remove the hooks and the logic around:

luatest/luatest/cluster.lua

Lines 351 to 353 in b446120

	hooks.before_all_preloaded(init)
	hooks.after_each_preloaded(drop)
	hooks.after_all_preloaded(clean)

The testing framework should be universal, but these hooks limit it to some specific case. As example, I can't:

1. I want to start 3 clusters and don't drop them between separate tests.
2. I want to start a single cluster of config storage for all tests.

As an alternative way: add a cluster option to be able to create a cluster without the logic.

[Totktonada]

I agree that a flexibility is wishful here. I would add a detach option that disables the autostop and allows to control the lifespan of the cluster object manually.

However, I would keep the default behavior intact, because I found it convenient after ~1 year of using this helper for writing various tests. It allows:

• reduce boilerplate code we have in each test
• let the testing framework bother about cleanup activities
• reduce chance that a developer forget about cleanup at all

I agree that this default doesn't handle all the possible situations, but it is convenient for many of them.