TooManyInterfaces from coreos docker image

[stephen-soltesz]

While running disco in a docker image from CoreOS for the first time (yay!) we found that:

/usr/lib/python2.6/site-packages/mlab/disco/network.py failed due to:

Traceback (most recent call last):
  File "/usr/bin/disco_config.py", line 106, in generate_collectd_snmp_config
    found_ports = discover_session.auto_discover_ifindex()
  File "/usr/lib/python2.6/site-packages/mlab/disco/discovery.py", line 106, in auto_discover_ifindex
    local_mac = network.get_local_mac()
  File "/usr/lib/python2.6/site-packages/mlab/disco/network.py", line 56, in get_local_mac
    'Multiple physical interfaces are not supported, found: %s' % macs)
TooManyInterfaces: Multiple physical interfaces are not supported, found: set(['e4:1d:2d:17:e7:81', 'e4:1d:2d:17:e7:80', '02:42:88:b3:04:6c'])

For an immediate work around, I just filtered the interfaces to only eth0:

>>> filter(lambda x: 'eth0' in x, netifaces.interfaces())

This needs a more general solution.