Add router association utility function
Add router association utility function

Add function to create an association between a router and a bgpvpn

Change-Id: I23449a0363f9d8f3c77ea3be1e104586d3c111d1
Signed-off-by: George Paraskevopoulos <97fa9f4b61869a8ee92863df90135c882f7b3aa0@intracom-telecom.com>

mywulin/functest,mywulin/functest,opnfv/functest,opnfv/functest