ebd68b3d1e
There are only four valid values for the migration_type filter when listing migrations so let's document them for the request parameter. Note that the API jsonschema validation does not restrict the values since the filter parameter pre-dated jsonschema validation for query parameters. Specifying an invalid value would just result in no results from the DB query. Change-Id: I7fee254edefd524633af62d80cb47009b1cf010b