[xenial] _get_systemd_service_status fails to parse systemd "failed" state

[Ricardo Bánffy]

During the MAAS startup process, due to a isc-dhcp.server bug, we got the service in a failed state (neither "active" nor "inactive").

Examining regiond's log, we got:

2016-01-20 10:35:43 [HTTPChannel,0,127.0.0.1] 500 Error - /MAAS/api/1.0/nodegroups/c1eccfbd-28e2-468c-83cb-12f92049c182/interfaces/eth1/
        Traceback (most recent call last):
          File "/usr/lib/python3/dist-packages/provisioningserver/twisted/web/wsgi.py", line 497, in run
            appIterator = self.application(self.environ, self.startResponse)
          File "/usr/lib/python3/dist-packages/django/core/handlers/wsgi.py", line 189, in __call__
            response = self.get_response(request)
          File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 227, in get_response
            response = get_response(request)
          File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 216, in get_response
            request, get_resolver(None), sys.exc_info())
        --- <exception caught here> ---
          File "/usr/lib/python3/dist-packages/maasserver/utils/views.py", line 201, in get_response
            return django_get_response(request)
          File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 325, in __exit__
            self.fire()
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 197, in wrapper
            return func(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/utils/async.py", line 195, in fire
            self._fire_in_reactor(hook).wait(LONGTIME)
          File "/usr/lib/python3/dist-packages/crochet/_eventloop.py", line 231, in wait
            result.raiseException()
          File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 368, in raiseException
            raise self.value.with_traceback(self.tb)
        provisioningserver.rpc.exceptions.CannotConfigureDHCP: DHCPv4 server failed to restart: Unable to parse the active state from systemd for service 'maas-dhcpd', active state reported as 'failed'.

The code in _get_systemd_service_status does not deal correctly with a "failed" state.

root@autopkgtest:~# systemctl status maas-dhcpd
● maas-dhcpd.service - MAAS instance of ISC DHCP server for IPv4
   Loaded: loaded (/lib/systemd/system/maas-dhcpd.service; enabled; vendor preset: enabled)
   Active: failed (Result: exit-code) since Wed 2016-01-20 10:35:43 EST; 26min ago
     Docs: man:dhcpd(8)
  Process: 13387 ExecStart=/bin/sh -ec INTERFACES=$(cat /var/lib/maas/dhcpd-interfaces); LEASES_FILE=/var/lib/maas/dhcp/dhcpd.leases; [ -e $LEASES_FILE ] || touch $LEASES_FILE; chown root:root /var/lib/maas/dhcp /var/lib/maas/dhcp/dhcpd.leases*; exec dhcpd -user dhcpd -group dhcpd -f -q -4 -pf /run/maas/dhcp/dhcpd.pid -cf /var/lib/maas/dhcpd.conf -lf $LEASES_FILE $INTERFACES (code=exited, status=1/FAILURE)
  Process: 13383 ExecStartPre=/bin/chown root:root /var/lib/maas/dhcp (code=exited, status=0/SUCCESS)
  Process: 13379 ExecStartPre=/bin/mkdir -p /var/lib/maas/dhcp (code=exited, status=0/SUCCESS)
  Process: 13377 ExecStartPre=/bin/chown root:root /run/maas/dhcp (code=exited, status=0/SUCCESS)
  Process: 13375 ExecStartPre=/bin/mkdir -p /run/maas/dhcp (code=exited, status=0/SUCCESS)
 Main PID: 13387 (code=exited, status=1/FAILURE)

Jan 20 10:35:43 autopkgtest dhcpd[13387]: If you think you have received this message due to a b...her
Jan 20 10:35:43 autopkgtest dhcpd[13387]: than a configuration issue please read the section on ...ing
Jan 20 10:35:43 autopkgtest dhcpd[13387]: bugs on either our web page at www.isc.org or in the R...ile
Jan 20 10:35:43 autopkgtest dhcpd[13387]: before submitting a bug. These pages explain the proper
Jan 20 10:35:43 autopkgtest dhcpd[13387]: process and the information we find helpful for debugging..
Jan 20 10:35:43 autopkgtest dhcpd[13387]:
Jan 20 10:35:43 autopkgtest dhcpd[13387]: exiting.
Jan 20 10:35:43 autopkgtest systemd[1]: maas-dhcpd.service: Main process exited, code=exited, s...LURE
Jan 20 10:35:43 autopkgtest systemd[1]: maas-dhcpd.service: Unit entered failed state.
Jan 20 10:35:43 autopkgtest systemd[1]: maas-dhcpd.service: Failed with result 'exit-code'.
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