The 'external_modules' attribute on a Spec, when read from a YAML
configuration file, may contain extra formatting that is lost when
that Spec is written-to/read-from JSON format. This was resulting in
a hashing instability (when the Spec was read back, it would report a
different hash). This commit adds a function which removes the extra
formatting from 'external_modules' as it is passed to the Spec in
__init__ to ensure a consistent hash.
fab2622a71