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.

This is to comply to a comment from @cznewt in
https://github.com/tcpcloud/salt-formula-heka/pull/24.

This patch replaces the "interface" collectd plugin by the "netlink" one. The
"netlink" plugin provides the same metrics as "interface" but plus other
metrics such as the number of dropped packets.