Fix broken navoidverify on Linux

For the same reasons as documented in nav.ipdevpoll.epollreactor2,
navoidverify seems to have stopped working (at least on Linux), due
to incompatibilites between the default epollreactor implementation
and pynetsnmp.

This change installs NAV's epollreactor2 in Twisted before any
of the twisted imports run and install the default reactor.

bin/navoidverify

@@ -22,6 +22,7 @@ NAV-monitored devices.
 
 from __future__ import print_function
 
+import platform
 import sys
 from itertools import cycle
 from argparse import ArgumentParser
@@ -30,6 +31,11 @@ from nav.bootstrap import bootstrap_django
 
 bootstrap_django(__file__)
 
+if platform.system() == "Linux":
+    from nav.ipdevpoll.epollreactor2 import install
+
+    install()
+
 from nav.ipdevpoll.snmp.common import snmp_parameter_factory, SnmpError
 from nav.models.manage import Netbox, ManagementProfile
 from nav.ipdevpoll.snmp import snmpprotocol, AgentProxy