Accept interfaces without address family or method

[bobbywatson3]

SUMMARY

Interfaces do not require address family or method to be set. Without this patch, this module cannot parse inventory files that don't have the address family or method set.
fixes #30768

ISSUE TYPE

• Bugfix Pull Request

COMPONENT NAME

interfaces_file

ANSIBLE VERSION

ansible 2.4.2.0
  config file = None
  configured module search path = [u'/root/.ansible/plugins/modules', u'/usr/share/ansible/plugins/modules']
  ansible python module location = /usr/lib/python2.7/site-packages/ansible
  executable location = /usr/bin/ansible
  python version = 2.7.13 (default, Dec 22 2016, 09:22:15) [GCC 6.2.1 20160822]

ADDITIONAL INFORMATION

Example interfaces file that triggers bug:

auto lo
iface lo inet loopback

auto eth0
iface eth0 inet dhcp

auto br0
iface br0

Error seen before change

TASK [Add interface option] ************************************************************************
fatal: [172.x.x.x]: FAILED! => {"changed": false, "module_stderr": "Shared connection to 172.x.x.x closed.\r\n", "module_stdout": "\r\nTraceback (most recent call last):\r\n  File \"/tmp/ansible_vhT1bm/ansible_module_interfaces_file.py\", line 385, in <module>\r\n    main()\r\n  File \"/tmp/ansible_vhT1bm/ansible_module_interfaces_file.py\", line 366, in main\r\n    lines, ifaces = read_interfaces_file(module, dest)\r\n  File \"/tmp/ansible_vhT1bm/ansible_module_interfaces_file.py\", line 177, in read_interfaces_file\r\n    return read_interfaces_lines(module, f)\r\n  File \"/tmp/ansible_vhT1bm/ansible_module_interfaces_file.py\", line 211, in read_interfaces_lines\r\n    iface_name, address_family_name, method_name = words[1:4]\r\nValueError: need more than 1 value to unpack\r\n", "msg": "MODULE FAILURE", "rc": 0}

After change:

TASK [Add interface option] ************************************************************************
ok: [172.x.x.x]

[ansibot]

cc @hryamzik
click here for bot help

[hryamzik]

Awesome, looks good for me. I'd also like to see tests for this case but that's not a show stopper.
shipit

[bobbywatson3]

Is this waiting on anything to be merged?

[hryamzik]

CC @gundalow

[gundalow]

Waiting for Shippable to run (currently stale_ci) then I'll merge & cherry-pick into stable-2.5

[hryamzik]

Thanks man!

[gundalow]

Merged into devel and cherry picked into stable-2.5
8e7b250