selftests: openvswitch: add an initial flow programming case

The openvswitch self-tests can test much of the control side of
the module (ie: what a vswitchd implementation would process),
but the actual packet forwarding cases aren't supported, making
the testing of limited value.

Add some flow parsing and an initial ARP based test case using
arping utility.  This lets us display flows, add some basic
output flows with simple matches, and test against a known good
forwarding case.

Signed-off-by: Aaron Conole <aconole@redhat.com>
Reviewed-by: Adrian Moreno <amorenoz@redhat.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>