pbulk: support chroots when running on a single host.
Set LOCAL_INCLUDE_DIR to LOCALBASE.
For non-multiarch don't append ARCH64_SUBDIR.
pbulk: add support for local_bulklog

This cleans up a previous patch which worked around issues writing
directly to bulklog over NFS.  By setting this variable we can write to
a local file system before moving to NFS at the end if necessary.