'Extract/link base_tree to self.build_dir'

def get_kernel_tree(self, base_tree):

    if os.path.isdir(base_tree):
        print 'Symlinking    existing    kernel    source'
        if os.path.islink(self.build_dir):
            os.remove(self.build_dir)
        os.symlink(base_tree, self.build_dir)
    else:
        os.chdir(os.path.dirname(self.src_dir))
        tarball = os.path.join(self.src_dir, os.path.basename(base_tree.split(';')[0]))
        utils.get_file(base_tree, tarball)
        print 'Extracting    kernel    tarball:', tarball, '...'
        utils.extract_tarball_to_dir(tarball, self.build_dir)
