scripts/bitbake: try harder to check if pseudo exists

scripts/bitbake: try harder to check if pseudo exists

If pseudodone doesn't exist, we can get STAGING_BINDIR_NATIVE by calling
bitbake -e and use that as the path to check for pseudo before we give
up and try to build it explicitly first.

This is useful for people who share TMPDIR between multiple build
directories.

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>