Tolerate bad environment until validation

Currently if we get a bad environment for a template_resource,
it causes an exception in the resource constructor, which does cause
the stack create to fail, but also all subsequent operations too.

By tolerating the error in the constructor, we can catch it instead at
validation time.

Change-Id: Ia971d8f1c50ca6f265ec36ea564aeba1638de541
Closes-Bug: 1227816
Merge "Tolerate bad environment until validation"