Fix byte check in tempest plugin

Different implementations of ping behave slightly differently
in order to ensure the packet payload is transmitted across
the wire because some mediums have a minimum packet size.

Typically this results in a frame size of 64 bytes, but
the client may report 56 when the header is removed and only
the packet payload is examined.

But the point of the check is that we got something back.

The below edited for example purposes:

$ ping -c1 -w4 192.168.133.92
PING 192.168.65.92 (192.168.133.92) 56(84) bytes of data.
From 192.168.65.249 icmp_seq=1 Destination Host Unreachable

--- 192.168.65.92 ping statistics ---
1 packets transmitted, 0 received, 0 errors, 100% packet loss, time 3075ms
$ ping -c1 -w4 192.168.65.1
PING 192.168.65.1 (192.168.65.1) 56(84) bytes of data.
64 bytes from 192.168.65.1: icmp_seq=1 ttl=64 time=12.4 ms

And then in CI, we're able to see this be 56 bytes returned
becasue the underlying medium may not have been ethernet or
the client has stripped the header. Which, doesn't matter,
we get A reply from the expected address and we can validate
the test on that alone.

Change-Id: If0d51b52e96f280336d0d92135681db75a6fbd65
2 files changed