Throw config error when using global zones as parent

[Crunsher]

Disallow global zones as parent

object Endpoint "foo" {
}

object Zone "fooz" {
	endpoints = [ "foo" ]
	parent = "global-templates"
}

object Zone "director-global" {
	global = true
}

used to be allowed, now this output is expected:

$ icinga2 daemon -C
[2018-06-15 14:43:03 +0200] information/cli: Icinga application loader (version: v2.8.4-748-gee9be90fa)
[2018-06-15 14:43:03 +0200] information/cli: Loading configuration file(s).
[2018-06-15 14:43:04 +0200] information/ConfigItem: Committing config item(s).
[2018-06-15 14:43:04 +0200] information/ApiListener: My API identity: jfws
[2018-06-15 14:43:05 +0200] critical/config: Error: Zone 'fooz' can not have a global zone as parent.
Location: in /home/jflach/i2/etc/icinga2/zones.conf: 33:1-33:18
/home/jflach/i2/etc/icinga2/zones.conf(31): }
/home/jflach/i2/etc/icinga2/zones.conf(32): 
/home/jflach/i2/etc/icinga2/zones.conf(33): object Zone "fooz" {
                                            ^^^^^^^^^^^^^^^^^^
/home/jflach/i2/etc/icinga2/zones.conf(34):  endpoints = [ "foo" ]
/home/jflach/i2/etc/icinga2/zones.conf(35):  parent = "global-templates"

[2018-06-15 14:43:05 +0200] critical/config: 1 error

[dnsmichi]

Will be merged after 2.9.