Make the template and env yaml parsing more consistent

in the environment_format.py use the same yaml_loader

Partial-bug: #1242155
Change-Id: I66b08415d450bd4758af648eaff0f20dd934a9cc
Add a test for TimeoutInMinutes accepting a str int

The nested stack resource should accept a number as a string
for TimeoutInMinutes.
The actual fix has been fixed by: https://review.openstack.org/#/c/52564/
but this just proves it.

Change-Id: I769a34eb536177b405a585158df383bbd3021cf9
Partial-bug: #1240903
Merge "Add a test for TimeoutInMinutes accepting a str int"
Merge "Make the template and env yaml parsing more consistent"