Create temporary dirs under compose's workdir
    
    Add compose.mkdtemp which creates and returns a unique temporary
    directory under <compose_topdir>/work/{global,<arch>}/tmp[-<variant>]/
    
    Change tempfile.mkdtemp in code to compose.mkdtemp, so temporary
    dirs are created under the compose's workdir, this makes it more
    easier to maintain the temporary dirs/files especially when compose
    fails with amount of temporary files left there.
    
    Signed-off-by: Qixiang Wan <qwan@redhat.com>