Use get_snmp_session_for_profile() in Arnold

Arnold mostly uses PortAdmin management handlers, except for when
changing the ifAdminStatus value of a port.

This lets the get_snmp_session_for_profile() utility function set up
these SNMP sessions instead, so that even SNMPv3 sessions will be
supported.

Additionally, to avoid mocking hell when updating the corresponding unit
tests, this inserts an optional argument for dependency injection, so a
caller (i.e. the test suite) can specify which utility function to use
to fetch an Snmp class.

python/nav/arnold.py

@@ -31,6 +31,7 @@
 from subprocess import Popen, PIPE
 from collections import namedtuple
 from smtplib import SMTPException
+from typing import Callable
 
 from IPy import IP
 from django.db import connection
@@ -40,6 +41,7 @@
 from nav.Snmp.errors import AgentError
 import nav.bitvector
 import nav.buildconf
+from nav.Snmp.profile import get_snmp_session_for_profile
 from nav.config import find_config_file
 from nav.errors import GeneralException
 from nav.models.arnold import Identity, Event
@@ -443,7 +445,11 @@ def open_port(identity, username, eventcomment=""):
     _logger.info("openPort: Port successfully opened")
 
 
-def change_port_status(action, identity):
+def change_port_status(
+    action,
+    identity,
+    agent_getter: Callable = get_snmp_session_for_profile,
+):
     """Use SNMP to change status on an interface.
 
     We use ifadminstatus to enable and disable ports
@@ -464,11 +470,7 @@ def change_port_status(action, identity):
     if not profile:
         raise NoReadWriteManagementProfileError
 
-    agent = nav.Snmp.Snmp(
-        host=netbox.ip,
-        community=profile.snmp_community,
-        version=profile.snmp_version,
-    )
+    agent = agent_getter(profile)(host=netbox.ip)
 
     # Disable or enable based on input
     try: