portable: Don't fail if /etc/resolv.conf doesn't exist

The portable profiles assume /etc/resolv.conf exists, which isn't
always the case. Let's mark the mounts as optional so we don't fail
to start the unit if /etc/resolv.conf doesn't exist.

Author: DaanDeMeyer

src/portable/profile/default/service.conf

@@ -4,7 +4,7 @@
 MountAPIVFS=yes
 BindReadOnlyPaths=/dev/log /run/systemd/journal/socket /run/systemd/journal/stdout
 BindReadOnlyPaths=/etc/machine-id
-BindReadOnlyPaths=/etc/resolv.conf
+BindReadOnlyPaths=-/etc/resolv.conf
 BindReadOnlyPaths=/run/dbus/system_bus_socket
 DynamicUser=yes
 RemoveIPC=yes

src/portable/profile/trusted/service.conf

@@ -5,4 +5,4 @@ MountAPIVFS=yes
 PrivateTmp=yes
 BindPaths=/run
 BindReadOnlyPaths=/etc/machine-id
-BindReadOnlyPaths=/etc/resolv.conf
+BindReadOnlyPaths=-/etc/resolv.conf