Fix #160

[bewing]

Update ping() for EOS to:
Strip trailing ':' from IP address
Check for truncated ECHO_RESPONSE and zero out RTT for that packet
Update normal test
Add truncated test

[bewing]

In [5]: d.ping("8.8.8.8")
Out[5]:
{u'success': {u'packet_loss': 0,
  u'probes_sent': 5,
  u'results': [{u'ip_address': u'8.8.8.8', u'rtt': 0.0},
   {u'ip_address': u'8.8.8.8', u'rtt': 0.0},
   {u'ip_address': u'8.8.8.8', u'rtt': 0.0},
   {u'ip_address': u'8.8.8.8', u'rtt': 0.0},
   {u'ip_address': u'8.8.8.8', u'rtt': 0.0}],
  u'rtt_avg': 24.72,
  u'rtt_max': 24.771,
  u'rtt_min': 24.667,
  u'rtt_stddev': 0.105}}

[coveralls]

Coverage increased (+0.05%) to 80.437% when pulling 77078be on bewing:iss160 into 67db8a0 on napalm-automation:develop.

[coveralls]

Coverage increased (+0.05%) to 80.437% when pulling 77078be on bewing:iss160 into 67db8a0 on napalm-automation:develop.

[bewing]

Writing another commit to address #162 as it only affects truncated packets, so don't merge yet

[coveralls]

Coverage increased (+0.3%) to 80.653% when pulling bd90dfc on bewing:iss160 into 67db8a0 on napalm-automation:develop.

[coveralls]

Coverage increased (+0.3%) to 80.653% when pulling bd90dfc on bewing:iss160 into 67db8a0 on napalm-automation:develop.

[coveralls]

Coverage increased (+0.3%) to 80.653% when pulling bd90dfc on bewing:iss160 into 67db8a0 on napalm-automation:develop.

[dbarrosop]

+1000 great use of the test cases :)