move expect into it-block for onto-controller spec

expect (and also response) should only be used inside of
an examples. Examples are the content of `it`-blocks.
`context`-blocks do not represent examples.
Merge pull request #808 from ontohub/fix_ontologies_controller_spec

move expect into it-block for onto-controller spec
clean redis-db namespace before each spec.
improve redis cleaning rake task method

Instead of calling delete for each key, we call
delete for all keys at once.