log_crypt_101_read_checkpoint(): Read the encryption information
from a MariaDB 10.1 checkpoint page.

log_crypt_101_read_block(): Attempt to decrypt a MariaDB 10.1
redo log page.

recv_log_format_0_recover(): Only attempt decryption on checksum
mismatch. NOTE: With the MariaDB 10.1 innodb_encrypt_log format,
we can actually determine from the cleartext portion of the redo log
whether the redo log is empty. We do not really have to decrypt the
redo log here, if we did not want to determine if the checksum is valid.