Raise VipExists exception in case Vip is created or updated
for a pool that already has a Vip

fixes bug 1158049

Change-Id: I258a31f5d54c040ed478ab241b0e90f2bd0f69b3
Merge "Raise VipExists exception in case Vip is created or updated for a pool that already has a Vip" into stable/grizzly