dataplane: copy buffer returned by pypcap

When reading packets pypcap always returns a pointer to the same statically
allocated memory, which will be overwritten the next time a packet is read. I
believe this is a bug in pypcap. The workaround is to make a copy immediately.
Merge into master from pull request #111:
update pyloxi to floodlight/loxigen-artifacts@6bc35bacb8ac44ebfc391b8bf9... (https://github.com/floodlight/oftest/pull/111)
Merge into master from pull request #110:
dataplane: copy buffer returned by pypcap (https://github.com/floodlight/oftest/pull/110)
remove broken openflow_protocol_messages.Hello

The handshake is already complete by the time this test sends a HELLO message.
Merge into master from pull request #113:
remove broken openflow_protocol_messages.Hello (https://github.com/floodlight/oftest/pull/113)
update pyloxi to floodlight/loxigen-artifacts@2bdcfd80f3a96740d1b3fb364eeee3d7bf420a8c