When running universe builds, we don't expect an error exit code for
provider warnings. Change the error messages to warnings in this case.
This deals with errors causing problems on our autobuilders amongst
other issues.
(Bitbake rev: d4989fb0355476de172169f0698757f7360e9a1f)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>