This patch enables availability zone reselected by stack retry
when "instantiate" "scale" "heal" operations in v2 API fails
due to availability zone is unavailable.
Note that precondition of using these functions is to use
StandardUserData as UserData class.
Implements: blueprint enhance-placement
Change-Id: Icc9eb7a8fffbf35d2e005a9703dcefe66f097584