Reworked instance_type parameter for heat section

Reworked instance_type parameter for heat section:
earlier due to PROD-24633 in case of Octavia, the
[heat]/instance_type parameter was missed because
only one flavor was fetched and it had not > 3 Gb
disk.
Since there is no possibility to fetch more than
1 item from the pillar (more than 1 flavor),
reworked the method to list flavors in Nova and
select correct one.

Change-Id: I615e4e068b33bfc840ac0f83b689cb2e80178e3a
Related-PROD: PROD-24633
1 file changed