PyYAML is efficient with YAML anchors and will only construct one
Python object for a YAML mapping that is used multiple times via
anchors.
We copy job variables (a mapping) straight from the YAML to an
attribute of the Job object, then we freeze the Job object which
converts all of its dicts to mappingproxy objects. This mutates
the contents of the vars dict, and if that is used on another
job via an anchor, we will end up with mappingproxy objects in
what we think is a "raw yaml" configuration dict, and we will not
be able to serialize it in case of errors.
To address this, perform a deep copy of every configuration yaml
blob before parsing it into an object.
Change-Id: Idaa6ff78b1ac5a108fb9f43700cf8e66192c43ce
James E. Blair
776bbc6a6e