Adding own child_template for AutoScalingGroup

Resource AutoScalingGroup fails during preview, because it uses the
parent child_template function with an invalid property Size. So
AutoScalingGroup should have its own child_template with correct
properties. Also new method child_template is used during handle_create.

Change-Id: I0068c1eaf19464c39348823160b665f538fec583
Closes-Bug: #1322583
Merge "Adding own child_template for AutoScalingGroup"