core: Asuswrt not showing any devices on 0.82.1.

Home Assistant release with the issue: 0.82.1

Last working Home Assistant release (if known): 0.81.6

Operating environment (Hass.io/Docker/Windows/etc.): Docker

Component/platform: Asuswrt device tracker

Description of problem: All device tracker entities show not_home whether they are connected or not. Reviewing debug logs shows several commands fail with error code 127 (command not found) although running these commands in an ssh terminal succeeds and provides expected output.

Problem-relevant configuration.yaml entries and (fill out even if it seems unimportant):

- platform: asuswrt
  host: 10.0.0.1
  protocol: ssh
  username: !secret router_user
  password: !secret router_pass
  track_new_devices: false
  consider_home: 180

Traceback (if applicable):

2018-11-15 13:42:51 INFO (MainThread) [homeassistant.components.device_tracker.asuswrt] Checking Devices
2018-11-15 13:42:51 DEBUG (MainThread) [asyncssh] [conn=0, chan=16] Set write buffer limits: low-water=16384, high-water=65536
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=16] Requesting new SSH session
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=16]   Command: for dev in `nvram get wl_ifnames`; do wl -i $dev assoclist; done
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=16] Received exit status 0
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=16] Received channel close
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=16] Channel closed
2018-11-15 13:42:51 DEBUG (MainThread) [asyncssh] [conn=0, chan=17] Set write buffer limits: low-water=16384, high-water=65536
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=17] Requesting new SSH session
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=17]   Command: arp -n
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=17] Received exit status 127
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=17] Received channel close
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=17] Channel closed
2018-11-15 13:42:51 DEBUG (MainThread) [asyncssh] [conn=0, chan=18] Set write buffer limits: low-water=16384, high-water=65536
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=18] Requesting new SSH session
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=18]   Command: ip neigh
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=18] Received exit status 127
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=18] Received channel close
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=18] Channel closed
2018-11-15 13:42:51 DEBUG (MainThread) [asyncssh] [conn=0, chan=19] Set write buffer limits: low-water=16384, high-water=65536
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=19] Requesting new SSH session
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=19]   Command: cat /var/lib/misc/dnsmasq.leases
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=19] Received exit status 0
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=19] Received channel close
2018-11-15 13:42:51 INFO (MainThread) [asyncssh] [conn=0, chan=19] Channel closed

Additional information: My current Asus setup is an RT-AC88U as my main router with an RT-AC68U connected over ethernet backhaul using AiMesh.