composer-cli uses TOML for 'blueprints save' which was returning an
empty 200 response if the blueprint didn't exist. Change this to return
a standard 400 error response if the blueprint doesn't exist.
composer-cli is already setup to handle receiving json when an error is
returned so just the toml API response for `blueprints/save` needed to
be changed.
these are built on top of beakerlib and we use its internal
protocol to figure out the result without relying on the full
test runner that is tipically used inside of a RHEL environment!
Includes a disabled test snippet for Issue #460