[spp] Remove spp_vm from SPP

[Yasufumi Ogawa]

Hi,

Spp_vm is a secondary process running on a Virtual Machine as spp_nfv. It was originally introduced for connecting between DPDK 
app running inside the VM and host with ring interfaces. It means that spp_vm communicate with host processes via IVSHMEM. 
However, IVSHMEM support in DPDK is suspended because of issues of mentainance, and it does not seem to be resumed.

Spp_vm is still able to be used to connect between apps in the VM, but it is almost the same as launching spp_primary and 
spp_nfv on the VM. Thanks for multi-node support recently introduced to SPP, we can manage several SPP nodes from one CLI 
terminal. It is time to remove spp_vm from SPP.

I would like to update SPP to remove spp_vm.

Thanks,
Yasufumi

-- 
Yasufumi Ogawa
NTT Network Service Systems Labs