Call ethtool directly (#630)

Trying to call /sbin/ethtool causes our job
networking/info_device(number)_(interface) to fail loading additional
information when Checkbox is installed as a snap, because in this case
the location of ethtool is /snap/checkbox22/current/sbin/ethtool

Calling ethtool directly to let the system handle the tool location.

Fix #508

providers/base/bin/network_device_info.py

@@ -39,7 +39,7 @@ class Utils():
  @staticmethod
  def get_ethtool_info(interface, key):
  """Return ethtool information identified by key"""
- cmd = ['/sbin/ethtool', interface]
+ cmd = ['ethtool', interface]
  try:
  output = check_output(cmd, stderr=STDOUT, universal_newlines=True)
  except CalledProcessError: