bench_env: Initial version of the benchmark environment setup

A set of test cases with the goal of measuring easily the peformance
between snabbswitch and virtual machines through vhost_user.

Included three main test cases:
- guest to guest:
    guest0 -> snabb nfv0 -> NIC0 = NIC1 <- snabb nfv1 <- guest1
- guest to host:
    guest0 -> snabb nfv0 -> NIC0 = NIC1 <- host
- guest to loadgen
    guest -> snabb nfv -> NIC_0 = NIC_1 <- snabb loadgen

Some helper scripts are also included:
- NIC rebinding
- guest to guest through vhost-tap

Signed-off-by: Alexander Spyridakis <a.spyridakis@virtualopensystems.com>
Added C.stat_mtime(filename) to check file modification time.
neutron2snabb: Script to convert Neutron database to snabb config.
neutron-sync-master: Added DB-sync script for Network Node.
neutron-sync-agent: Added DB sync script for Compute Nodes.
Added snabbnfv-traffic traffic handling process script.
Made Neutron scripts executable.
Add config.graphviz(c) to create a graphviz diagram.

This is handy for sanity-checking app networks by eye.
packet_filter: Accept 'rx' and 'tx' as port names too.
packet.lua: Fix broken clone().
main.exit(): Fixed bug - always used exit status 0.
socket/dev.lua: Updated after packet.lua API change.
ns_responder: Make north->south direction optional.

Use packet.want_modify().
packet.h: buffer data is now 'unsigned char *' (was char *)
app.lua: Fixed typo s/monotinic_now/monotonic_now/.

Closes #183.
Merge pull request #185 from virtualopensystems/master

benchmark environment setup
Merge pull request #180 from lukego/neutron

Add OpenStack Neutron agents
Merge pull request #181 from lukego/fixes

Miscellaneous bug fixes
virtio netdevice: optimize map_from_guest

Optimize map_from_guest to store the last found element on the
0-th position for faster finding later.

Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>
memory: optimize virtual_to_physical

A further optimization to virtual_to_physical.

Signed-off-by: Nikolay Nikolaev <n.nikolaev@virtualopensystems.com>