The idea here is to make sure all return points have the same type for
the error cases. There's not really all that many, so they just go in
one patch. Some of these could potentially turn into more specialized
errors later.
Note the exception string checking around compose_type. I didn't really
want to introduce a new exception type just for this, but also didn't
want to duplicate strings. I'd be open to other suggestions for how to
do this.
This adds some fairly redundant code to the beginning of all the
blueprint routes to attempt reading a commit from git for the
blueprint's recipe. If it succeeds, the blueprint exists and the route
can continue. Otherwise, return an error. Hopefully this doesn't slow
things down too much.
Note that this also changes the return type of uuid_info to return None
when an unknown ID is given. The other uuid_* functions are fine
because they are checked ahead of time.
Each element in the errors value is now a dict, with a msg field and an
id field. The id field contains a value out of errors.py that can be
used by the front end to key on. The msg field is the same as what's
been there.
The idea is to keep the number of IDs somewhat limited so there's not a
huge number of things for the front end to know.
