fixes for antlir2

Summary:

antlir2 builds never have a booted systemd as pid1, so any dbus interactions will fail

This diff no-ops:
- `daemon-reload`
- `daemon-reexec`

and branches with `--root=/` for:
- `set-default`

Differential Revision: D48618221

fbshipit-source-id: 4cecc50040bcbae7325063bdca7e1c9fffd07868

cookbooks/fb_systemd/metadata.rb

@@ -13,3 +13,4 @@
 supports 'arch'
 depends 'fb_helpers'
 depends 'fb_nsswitch'
+depends 'fb_util'

cookbooks/fb_systemd/recipes/default.rb

@@ -159,15 +159,19 @@
 
 execute 'set default target' do
   only_if do
-    current = shell_out('systemctl get-default').stdout.strip
+    if node.antlir2_build?
+      current = shell_out('systemctl --root=/ get-default').stdout.strip
+    else
+      current = shell_out('systemctl get-default').stdout.strip
+    end
     is_ignored = node['fb_systemd']['ignore_targets'].include?(current)
     is_supported = FB::Version.new(node['packages']['systemd'][
       'version']) >= FB::Version.new('205')
     is_supported && !is_ignored &&
       current != node['fb_systemd']['default_target']
   end
   command lazy {
-    "systemctl set-default #{node['fb_systemd']['default_target']}"
+    "systemctl set-default #{node['fb_systemd']['default_target']} #{node.antlir2_build? ? '--root=/' : ''}"
   }
 end
 

cookbooks/fb_systemd/resources/reload.rb

@@ -34,6 +34,10 @@ def daemon_reload_or_reexec(action)
       )
       return
     end
+    # Image builds don't have a running systemd, that would make no sense
+    if node.antlir2_build?
+      return
+    end
     case new_resource.instance
     when 'system'
       execute "#{action} systemd system instance" do