VNF interfaces are sorted by "vpci" address before being populated

VNF interfaces are sorted by "vpci" address before being populated

In [1], VNF interfaces in TG PROX are sorted by "vpci" address, before
this value is populated in "vnfd_helper". "vpci_if_name_ascending" is
only used in TP ProxPofile [2] to generate the stats.

This patch delays this sorting process until the stats generation.

[1]https://github.com/opnfv/yardstick/blob/a74ad5a1ec1a73389c5983440b2031b0bc72cea1/yardstick/network_services/vnf_generic/vnf/tg_prox.py#L62-L64
[2]https://github.com/opnfv/yardstick/blob/a74ad5a1ec1a73389c5983440b2031b0bc72cea1/yardstick/network_services/traffic_profile/prox_profile.py#L33

JIRA: YARDSTICK-1044

Change-Id: I988dc48f9a82baa1c64f728d9e6d54f2f4bae010
Signed-off-by: Rodolfo Alonso Hernandez <rodolfo.alonso.hernandez@intel.com>