Taking host health into account when picking host

[Denchick]

Is your feature request related to a problem? Please describe. In #813 was introduced availability zones. But this feature does not take into account the health of the hosts in any way. Like network delays.

Describe the solution you'd like It seems that we can't measure a "real" ping (at least that's what they say on the Internet). But it seems that SELECT 1 will be enough for now.