block: deprecate "encryption=on" in favor of "encrypt.format=aes"

block: deprecate "encryption=on" in favor of "encrypt.format=aes"

Historically the qcow & qcow2 image formats supported a property
"encryption=on" to enable their built-in AES encryption. We'll
soon be supporting LUKS for qcow2, so need a more general purpose
way to enable encryption, with a choice of formats.

This introduces an "encrypt.format" option, which will later be
joined by a number of other "encrypt.XXX" options. The use of
a "encrypt." prefix instead of "encrypt-" is done to facilitate
mapping to a nested QAPI schema at later date.

e.g. the preferred syntax is now

  qemu-img create -f qcow2 -o encrypt.format=aes demo.qcow2

Signed-off-by: Daniel P. Berrange <[email protected]>
Message-id: 20170623162419[email protected]
Reviewed-by: Alberto Garcia <[email protected]>
Signed-off-by: Max Reitz <[email protected]>