Checkable: Don't skip redundancy group checks for parent dependencies

[yhabteab]

Previously, all parent dependencies were recursively checked right at the beginning of Checkable::IsReachable() for reachability and immediately returned false if one of them fails. However, since the introduction of redundancy_group, that failed parent might be within a redundancy group, which shouldn't necessarily cause the dependency to fail completely. This PR changes this insofar as not all parents are checked at the beginning of the method, but only a single parent per a dependency object is evaluated.

Tests

Icinga 2 Config

include <itl>

object CheckerComponent "checker" {}
object ApiListener "api" {}

object ApiUser "root" {
  password = "icinga"
  permissions = [ "*" ]
}

template Host "default" default {
	check_command = "dummy"
	max_check_attempts = 1
	check_interval = 10s

	vars.dummy_state = 0
	vars.dummy_text = "I'm just testing something"
}

object Host "paternal_grandfather" {
    vars.dummy_state = 2
}
object Host "maternal_grandfather" {}
object Host "father" {}
object Host "mother" {
    vars.dummy_state = 2
}
object Host "son" {}

object Dependency "paternal_grandfather" {
    parent_host_name = "paternal_grandfather"
    child_host_name = "father"
}

object Dependency "father" {
    parent_host_name = "father"
    child_host_name = "son"
    redundancy_group = "parents"
}
object Dependency "mother" {
    parent_host_name = "mother"
    child_host_name = "son"
    redundancy_group = "parents"
}

Before

<63> => get_host("paternal_grandfather").last_check_result.state
2.000000
<64> => get_host("father").last_check_result.vars_after.reachable
false
<65> => get_host("mother").last_check_result.state
2.000000
<66> => get_host("son").last_check_result.vars_after.reachable
false

Now, change the dummy state for the mother Host to vars.dummy_state = 0.

<55> => get_host("paternal_grandfather").last_check_result.state
2.000000
<56> => get_host("father").last_check_result.vars_after.reachable
false
<57> => get_host("mother").last_check_result.state
0.000000
<58> => get_host("son").last_check_result.vars_after.reachable
false

After

<30> => get_host("paternal_grandfather").last_check_result.state
2.000000
<31> => get_host("father").last_check_result.vars_after.reachable
false
<32> => get_host("mother").last_check_result.state
2.000000
<33> => get_host("son").last_check_result.vars_after.reachable
false

Now, change the dummy state for the mother Host to vars.dummy_state = 0.

<40> => get_host("paternal_grandfather").last_check_result.state
2.000000
<41> => get_host("father").last_check_result.vars_after.reachable
false
<42> => get_host("mother").last_check_result.state
0.000000
<43> => get_host("son").last_check_result.vars_after.reachable
true

fixes #10014

[Al2Klimov]

Admittedly other construction area, but while on it, you could increment rstack just once before the loop.

[yhabteab]

Ah, because currently the sum of all direct and intermediate dependencies is limited to 256. You want me to change this so that the limit applies to each dependency object individually? I can do this, but as you already said, it's not related to this issue.

[Al2Klimov]

LGTM

[yhabteab]

Superseded by #10290.