heat engine : Autoscaling reload Loadbalancer correctly

Since the change implemented as part of bug #1136148 we no longer
wait for nova to create the instance before reloading the loadbalancer
which means we race nova assigning an IP to the instance and typically
the loadbalancer config ends up with the 0.0.0.0 default value
which the loadbalancer implementation uses when nova returns no IP.

This patch moves the LB reload into a separate function, which is called
after instances are active on group creation or adjustment

Since our loadbalancer is broken without this fix, this is a candidate
for backporting to grizzly milestone-proposed.

fixes bug #1160407

Change-Id: I50423883dead9a615aa79b8765d5480a9345686d