Previously, baseurl was required in openapi.yaml. In order to add support
for metalink and mirrorlist repos as well, make all optional, since openapi
does not support mutually exclusive parameters. Instead, enforce this logic
in server.go, and if no repo has been specified, return a 400 bad request error.
Don't use common.State anymore, because it has different values from
what's defined in openapi.yml. It makes sense to have these strings
defined in the same package as the spec — ideally, the code generator
would make them for us.
While at it, add a "running" status.
Fix the api.sh test to use these new statuses. Thanks to Ondřej Budai
for an additional fix there.
