Don't reboot the system when serial port is not detected properly

Change-Id: I3e691166d67d528365710cdb25ad64888a565b85
diff --git a/edge-monitoring/agent_modem/edge-mon-agent.service b/edge-monitoring/agent_modem/edge-mon-agent.service
index c7c4d50..8f80c05 100644
--- a/edge-monitoring/agent_modem/edge-mon-agent.service
+++ b/edge-monitoring/agent_modem/edge-mon-agent.service
@@ -7,6 +7,7 @@
 Type=simple
 ExecStart=/home/pi/Aether/aether-monitoring/edge-monitoring/agent_modem/edge_monitoring_agent_modem.py
 Restart=on-failure
+ExecStartPre=/bin/sleep 5
 
 [Install]
 WantedBy=multi-user.target