Migrate addhost.php to lnms device:add (#13870)

* Migrate addhost.php to lnms device:add
Have snmp-scan.py call lnms device:add (make exit codes line up so this works)
Fix issue with ping only devices trying to detect os via snmp
Reorder options in device:add help and improve formatting
Update docs to remove references to addhost.php
Fix a bit of code that was in functional code

* fixes

* fix snmp version message

snmp-scan.py

@@ -128,8 +128,8 @@ def scan_host(scan_ip):
 
             arguments = [
                 "/usr/bin/env",
-                "php",
-                "addhost.php",
+                "lnms",
+                "device:add",
                 "-g",
                 POLLER_GROUP,
                 hostname or scan_ip,
@@ -261,7 +261,7 @@ Example: """
     networks = []
     for net in netargs if netargs else CONFIG.get("nets", []):
         try:
-            networks.append(ip_network(u"%s" % net, True))
+            networks.append(ip_network("%s" % net, True))
             debug("Network parsed: {}".format(net), 2)
         except ValueError as e:
             parser.error("Invalid network format {}".format(e))