HI !
As far as I know the current public available versions of the vMX do NOT support EVPN/VXLAN.
if you want to play with EVPN/VXLAN-L3 you need either a physical MX (junos version 14.2R7.5) or a vQFX10k
regards
alexander
PS maybe sone Juniper guy can confirm on that
PPS: Please have a look into the separate vMX forum -- and maybe transfer you post there