oeqa/selftest/bbtests: Add uuid to force build test

oeqa/selftest/bbtests: Add uuid to force build test

With hash equivalence working properly, this test breaks as it detects
an unchanged tasks and doesn't rerun subsequent tasks.

Add a uuid to the payload to ensure it doesn't ever match
equivalence and the test works as intended.

Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>