Fixes also MDEV-13488: InnoDB writes CRYPT_INFO even though
encryption is not enabled.

Fixes also MDEV-13093: Leak of Datafile::m_crypt_info on
shutdown after failed startup.

Problem was that we created encryption metadata (crypt_data) for
system tablespace even when no encryption was enabled and too early.
System tablespace can be encrypted only using key rotation.

Test innodb-key-rotation-disable, innodb_encryption, innodb_lotoftables
require adjustment because INFORMATION_SCHEMA INNODB_TABLESPACES_ENCRYPTION
contain row only if tablespace really has encryption metadata.

xb_load_single_table_tablespace(): Do not call
fil_space_destroy_crypt_data() any more, because Datafile::m_crypt_data
has been removed.

fil_crypt_realloc_iops(): Avoid divide by zero.

fil_crypt_set_thread_cnt(): Set fil_crypt_threads_event if
encryption threads exist. This is required to find tablespaces
requiring key rotation if no other changes happen.

fil_crypt_find_space_to_rotate(): Decrease the amount of time waiting
when nothing happens to better enable key rotation on startup.

fil_ibd_open(), fil_ibd_load(): Load possible crypt_data from first
page.

class Datafile, class SysTablespace : remove m_crypt_info field.

Datafile::get_first_page(): Return a pointer to first page buffer.

fsp_header_init(): Write encryption metadata to page 0 only if
tablespace is encrypted or encryption is disabled by table option.

i_s_dict_fill_tablespaces_encryption(): Skip tablespaces that do not
contain encryption metadata. This is required to avoid too early
wait condition trigger in encrypted -> unencrypted state transfer.