Align Keyring encryption and default_table_encryption

Currently default_table_encryption can be set to one of the values:

(1)OFF,(2)ON,(3)KEYRING_ON,(4)ONLINE_TO_KEYRING, (5)ONLINE_FROM_KEYRING_TO_UNENCRYPTED.

Setting one of those options when creating table/tablespace:

(1.1) should follow the current behavior, i.e. table/tablespace should have implicit ENCRYPTION='N' assigned
(1.2) ON :  Should follow the current behavior (i.e. assign ENCRYPTION='Y' if it was not assigned explicitly)
(1.3) Should assign ENCRYPTION='KEYRING' to table/tablespace
(1.4) Newly created tables/tablespaces should be created with crypt_data in page0, encryption set to FIL_ENCRYPTION_DEFAULT. This tables should be encrypted from the beginning, but it should be possible to decrypt them by encryption threads. This is the current behavior.
(1.5) Should follow (1.1) - current behavior.

DEFAULT ENCRYPTION schema option should support new value 'KEYRING':
When default_table_encryption is set to :
(2.1) ONLINE_TO_KEYRING new schemas will be created with DEFAULT ENCRYPTION=OFF, however the tables created in the schema will be created as in (1.4) - it should be the current behavior - need to double check this.
(2.2) ONLINE_FROM_KEYRING_TO_UNENCRYPTED new schemas will be created with implicit ENCRYPTION='N' (current behavior).

Make sure that this ticket covers:
ts1 is keyring encrypted by background thread and then CREATE TABLE t1(a INT) ENCRYPTION=KEYRING TABLESPACE=ts1 <- ENCRYPTION='KEYRING' should not be possible, the same for ALTER.