ibuf_check_bitmap_on_import(): Only access the pages that
are below FSP_FREE_LIMIT. It is possible that especially with
ROW_FORMAT=COMPRESSED, the FSP_SIZE will be much bigger than
the FSP_FREE_LIMIT, and the bitmap pages (page_size*N, 1+page_size*N)
are filled with zero bytes.

buf_page_is_corrupted(), buf_page_io_complete(): Make the
fault injection compatible with MariaDB 10.2.

Backport the IMPORT tests from 10.2.