miq_qe - support debounced.cancel, debounced.flush
miq_qe - support debounced.cancel, debounced.flush

when using _.debounce, the debounced function has 2 extra methods (described in https://github.com/lodash/lodash/blob/master/debounce.js#L7-L9):

* cancel - cancels the call
* flush - triggers the call if it was pending

but the QE wrapper is currently not returning either of these.
Fixing :).

`cancel` needs to clean the debounce registry becuase the function will never get called.
`flush` doesn't, because the function does get called.

ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic,ManageIQ/manageiq-ui-classic