launch: avoid autostarting pulseaudio systemd units for root

The autospawn mechanism already had a root-autospawn protection mechanism. When
using systemd that was lost. Systemd 234 has a mechanism to conditionalize unit starting
on the running user, so lets do that to protect against root autospawning.

src/daemon/systemd/user/pulseaudio.service.in

@@ -14,6 +14,7 @@ Description=Sound Service
 # After=pulseaudio.socket is not needed, as it is already implicit in the
 # socket-service relationship, see systemd.socket(5).
 Requires=pulseaudio.socket
+ConditionUser=!root
 
 [Service]
 # Note that notify will only work if --daemonize=no

src/daemon/systemd/user/pulseaudio.socket

@@ -1,5 +1,6 @@
 [Unit]
 Description=Sound System
+ConditionUser=!root
 
 [Socket]
 Priority=6