crypto: add support for the twofish cipher algorithm

New cipher algorithms 'twofish-128', 'twofish-192' and
'twofish-256' are defined for the Twofish algorithm.
The gcrypt backend does not support 'twofish-192'.

The nettle and gcrypt cipher backends are updated to
support the new cipher and a test vector added to the
cipher test suite. The new algorithm is enabled in the
LUKS block encryption driver.

Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
diff --git a/qapi/crypto.json b/qapi/crypto.json
index 6738b95..63c001a 100644
--- a/qapi/crypto.json
+++ b/qapi/crypto.json
@@ -63,6 +63,9 @@
 # @serpent-128: Serpent with 128 bit / 16 byte keys
 # @serpent-192: Serpent with 192 bit / 24 byte keys
 # @serpent-256: Serpent with 256 bit / 32 byte keys
+# @twofish-128: Twofish with 128 bit / 16 byte keys
+# @twofish-192: Twofish with 192 bit / 24 byte keys
+# @twofish-256: Twofish with 256 bit / 32 byte keys
 # Since: 2.6
 ##
 { 'enum': 'QCryptoCipherAlgorithm',
@@ -70,7 +73,8 @@
   'data': ['aes-128', 'aes-192', 'aes-256',
            'des-rfb',
            'cast5-128',
-           'serpent-128', 'serpent-192', 'serpent-256']}
+           'serpent-128', 'serpent-192', 'serpent-256',
+           'twofish-128', 'twofish-192', 'twofish-256']}
 
 
 ##