Travis: Remove sleep test from integratorcp_cm926ejs-qemu test

Most of the time when running the sleep test in Travis for
the integratorcp_cm926ejs target I get errors like this:

  E       assert 2.999901056289673 >= 3

The deviation is tiny, but fails the overall build result. Since
the sleep test is not terribly important as gate keeper for travis
tests, let's just exclude it for this board.

Signed-off-by: Alexander Graf <agraf@suse.de>
Reviewed-by: Tom Rini <trini@konsulko.com>