Create the rpm build tree

def _mk_tree(runas='root'):
    '''
    Create the rpm build tree
    '''
    basedir = tempfile.mkdtemp()
    paths = ['BUILD', 'RPMS', 'SOURCES', 'SPECS', 'SRPMS']
    for path in paths:
        full = os.path.join(basedir, path)
        __salt__['file.makedirs_perms'](name=full, user=runas, group='mock')
    return basedir