Start OS Agent Systemd service after sysinit.target (home-assistant#224)

As OS Agent accesses various system features, it should be mandatory
that all mounts have been created and the system is mostly initialized.
This should be the sysinit.target - at this point everything should be
up and only various services should be being initialized (those would
need to be specified explicitly).

A concrete example of this target being needed is
systemd-sysctl.service - without that finished, OS Agent may get wrong
kernel parameters which are later set via that service.

Author: sairon

contrib/haos-agent.service

@@ -2,7 +2,7 @@
 Description=Home Assistant OS Agent
 DefaultDependencies=no
 Requires=dbus.socket udisks2.service
-After=dbus.socket
+After=dbus.socket sysinit.target
 
 [Service]
 BusName=io.hass.os