All environment variables that are not in the list returned by
preserved_envvars_exported are cleaned by bb.utils.clean_environment.
Added BBSERVER to the list as we need to access it in bb/main.py
after the call of bb.utils.clean_environment.
(Bitbake rev: 15c4ea679f4fe097a9f21cccfc82907b5f39a4e4)
Signed-off-by: Ed Bartosh <ed.bartosh@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>