Allow empty sections in the yaml templates

Existing check for absent sections in template is not enough for
handling situation with empty content.
Current patch improves using default value for parameters, resources and
outputs sections in yaml templates.

Change-Id: I94b572bf5f5b1593276616d9d0a84386dd12b8fe
Closes-Bug: #1312114
Merge "Allow empty sections in the yaml templates"