Quoting empty braces inside jinja blocks (i.e. {{ '{}' }}) tells jinja to treat
the braces as a string instead of as an empty dict. Since these occur in jinja
blocks, the yaml processor has already interpretted them as strings, and there is
no threat of the yaml processor interpretting the braces as a yaml object.
As-is, the quoted strings cause errors such as:
FAILED! => {"failed": true, "msg": "|combine expects dictionaries, got '{}'"}
Change-Id: I4f859d8e3b9eff7ce962d7690c1ceea3e6229fe5
f52ca4e8b5