Add option to pass in a nice option to the bitbake command

OpenBMC CI infrastructure has compute nodes that both run
bitbake and run QEMU CI sessions. QEMU only uses a single
core but it is very CPU dependent and so timeouts and
other issues can occur when competing with a bitbake
build. Adding a nice option for the bitbake operations
will allow us to ensure the QEMU session (or anything
else of priority on the shared compute node) gets priority

Signed-off-by: Michael Shepos <shepos@us.ibm.com>
Change-Id: Ide62d4cc7cd984f490bcae7f86eba6a645182b65
1 file changed