Fix the current zone master log message.

Fixes #6241
Fix cluster check output.

Fixes #6244
Documentation: Move ITL/Plugin Commands into Icinga 2 configuration.

Fixes #6245
Documentation: Add a better example for apply rules in monitoring basics.

Refs #5827
Documentation: Add a note on recovery notifications during downtime.

Refs #6228
Remove build dependency for postgresql84.

Fixes #5847
Documentation: Fix cluster config examples.

Fixes #6247
Documentation: Add a note for the vagrant demo vm to 'about' .

Fixes #6248
Test.