Make the IPAM endpoint versioned (/contiv/v1/)
Make the IPAM endpoint versioned (/contiv/v1/)

- Add new prefix const to rest_handlers that contains versioned prefix
for the REST endpoints
- Make /ipam endpoint use new versioned prefix (so now it is
/contiv/v1/ipam)

Signed-off-by: Tomas Slusny <71c4488fd0941e24cd13e3ad13ef1eb0a5fe5168@gmail.com>

rastislavszabo/vpp,milanlenco/vpp-1,rastislavszabo/vpp,milanlenco/vpp-1,brecode/vpp,brecode/vpp,rastislavszabo/vpp,rastislavszabo/vpp,milanlenco/vpp-1,brecode/vpp,rastislavszabo/vpp,rastislavszabo/vpp,brecode/vpp,brecode/vpp,milanlenco/vpp-1,rastislavszabo/vpp,milanlenco/vpp-1