NXD lib/tasks/gitlab/check: Exit with non-zero code, if something failed in a check task

This is handy for monitoring tools, which could e.g. periodically call check
tasks and instead of parsing output, rely on exit code.

The way we detect if something failed is via hooking into String#red, and if
anything was ever printed in red - that's an error.

lib/system_check/helpers.rb

@@ -2,6 +2,17 @@ module SystemCheck
   module Helpers
     include ::Gitlab::TaskHelpers
 
+    # if we ever print anything in red - that's an error
+    $check_failed = false
+    class String
+
+      alias_method :orig_red, :red
+      def red(*args)
+        $check_failed = true
+        orig_red(*args)
+      end
+    end
+
     # Display a message telling to fix and rerun the checks
     def fix_and_rerun
       $stdout.puts '  Please fix the error above and rerun the checks.'.color(:red)
@@ -24,8 +35,9 @@ module SystemCheck
     # @deprecated This will no longer be used when all checks were executed using SystemCheck
     def finished_checking(component)
       $stdout.puts ''
-      $stdout.puts "Checking #{component.color(:yellow)} ... #{'Finished'.color(:green)}"
+      $stdout.puts "Checking #{component.color(:yellow)} ... #{$check_failed ? "Failed".color(:red) : "OK".color(:green)}"
       $stdout.puts ''
+      exit 1 if $check_failed
     end
 
     # @deprecated This will no longer be used when all checks were executed using SystemCheck

lib/system_check/simple_executor.rb

 module SystemCheck
+
+  # if we ever print anything in red - that's an error
+  $check_failed = false
+  class String
+
+    alias_method :orig_red, :red
+    def red(*args)
+      $check_failed = true
+      orig_red(*args)
+    end
+  end
+
   # Simple Executor is current default executor for GitLab
   # It is a simple port from display logic in the old check.rake
   #
@@ -116,8 +128,9 @@ module SystemCheck
     # @param [String] component name of the component relative to the checks being executed
     def finished_checking(component)
       $stdout.puts ''
-      $stdout.puts "Checking #{component.color(:yellow)} ... #{'Finished'.color(:green)}"
+      $stdout.puts "Checking #{component.color(:yellow)} ... #{$check_failed ? "Failed".color(:red) : "OK".color(:green)}"
       $stdout.puts ''
+      exit 1 if $check_failed
     end
   end
 end