Adds SFC CRUD interface to the VIM connector

Change vimconn.py to include the interface functions
to be implemented by the specific VIM connectors, in order
to achieve Service Function Chaining as managed by a VIM.

This relates to feature 638.

Change-Id: I3b5c35ad5b2ca6e4cdd17e5720fbaa13acffc4e1
Signed-off-by: Igor Duarte Cardoso <igor.duarte.cardoso@intel.com>