There are several copy-pasted code fragments in impl QcowFile. All of
them add L2 entry to the cache and one of them (in file_offset_write())
does also allocating new L2 entry if necessary.
Fold all these code fragments (except of one in l2_table() which does
error handling in special way) into cache_l2_cluster() method without
changing the logic.
This will make the code more compact and clean.
Signed-off-by: Eugene Korenevsky <ekorenevsky@aliyun.com>
3791062b23