Use Pillar to chose which interfaces to monitor.

The `linux_netlink.ls` function used a regex to choose which interfaces
to collect metric for.

`_alphanum_re = re.compile(r'^[a-z0-9]+$')`

Unfortunately, by default this excludes vlan and tap interfaces, which
are kind of important.  ie `bond0.120` or `tap2a3dab86-fb`.

We also have a problem where even if we update the regex to include
these interfaces... if someone deletes and spawns a new instance then
the tap device name changes on the compute host, which will not be
monitored unless someone re-runs the `collectd` on the compute again.
Less than ideal.

This commit lets us choose `VerboseInterface "all"` using Pillar data
to avoid this problem.

_modules/linux_netlink.py

-# -*- coding: utf-8 -*-
-
-import re
-
-_alphanum_re = re.compile(r'^[a-z0-9]+$')
-_lo_re = re.compile(r'^lo$')
-
-
-def _filter(interface):
-    return _alphanum_re.match(interface) and not _lo_re.match(interface)
-
-
-def ls():
-    """
-    Provide a list of network interfaces.
-    """
-    return filter(_filter, __salt__['grains.get']('ip_interfaces', {}).keys())

linux/map.jinja

 {% set monitoring = salt['grains.filter_by']({
     'default': {
         'zombie': {
-              'warn': 3,
-              'crit': 7,
+            'warn': 3,
+            'crit': 7,
         },
         'procs': {
-              'warn': 5000,
-              'crit': 10000,
+            'warn': 5000,
+            'crit': 10000,
         },
         'load': {
-              'warn': '6,4,2',
-              'crit': '12,8,4',
+            'warn': '6,4,2',
+            'crit': '12,8,4',
         },
         'swap': {
-              'warn': '50%',
-              'crit': '20%',
+            'warn': '50%',
+            'crit': '20%',
         },
         'disk': {
-              'warn': '15%',
-              'crit': '5%',
+            'warn': '15%',
+            'crit': '5%',
+        },
+        'netlink': {
+            'interfaces': ['all'],
+            'ignore_selected': False,
         },
     },
 }, grain='os_family', merge=salt['pillar.get']('linux:monitoring')) %}

linux/meta/collectd.yml

+{%- from "linux/map.jinja" import monitoring with context %}
 local_plugin:
   linux_network_netlink:
     plugin: netlink
     template: linux/files/collectd_netlink.conf
-    ignore_selected: false
-    {%- if 'linux_netlink.ls' in salt.keys() %}
+    ignore_selected: {{ monitoring.netlink.ignore_selected }}
     interfaces:
-    {%- for interface_name in salt['linux_netlink.ls']() %}
+    {%- for interface_name in monitoring.netlink.interfaces|sort %}
     - {{ interface_name }}
     {%- endfor %}
     {%- endif %}