tests: improve efl loop test (concentric)

tests: improve efl loop test (concentric)

I forgot to spin the sub-loop, so this was previously just a test to verify
that the IDLE callback was working.

now this spins the sub-loop on the idle callback and tests the idle enter
callback to verify that the main loop is being iterated

Reviewed-by: Derek Foreman <derekf@osg.samsung.com>
Differential Revision: https://phab.enlightenment.org/D7874