system-dpdk: Connect network namespaces via dpdkvhostuser ports

system-dpdk: Connect network namespaces via dpdkvhostuser ports

This adds a few unit tests to the 'check-dpdk' subsystem that will
exercise allocations of two network namespaces, PMDs, and the
vhost-user and vhost-user-client code path(separate tests).
As part of the tests, userspace bridge is added and attached to OVS.
Also, the tap devices created are added to the network namespaces.

The ultimatum is to connect the two network namespaces by pinging them.

Signed-off-by: Bala Sankaran <bsankara@redhat.com>
Co-authored-by: Aaron Conole <aconole@redhat.com>
Signed-off-by: Aaron Conole <aconole@redhat.com>
Acked-by: Tiago Lam <tiago.lam@intel.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>