Increase heat's default max_template_size

devstack has a small 10k max template size.  This is too small for
many templates that may be used during development.  Thus, we need
to change this and devstack to a larger value.

Change-Id: I474c7cbc196a4e94ba67cab4e2ca2263dc902e26
Merge "Increase heat's default max_template_size"