MDEV-31474 KDF() function

KDF(key_str, salt [, {info | iterations} [, kdf_name [, width ]]])

kdf_name is "hkdf" or "pbkdf2_hmac" (default).

width (in bits) can be any number divisible by 8,
by default it's taken from @@block_encryption_mode

iterations must be positive, and is 1000 by default

OpenSSL 1.0 doesn't support HKDF, so it'll return NULL.
This OpenSSL version is still used in SLES 12 and CentOS 7

mysql-test/suite.pm

@@ -84,6 +84,8 @@ sub skip_combinations {
   $skip{'main/ssl_7937.combinations'} = [ 'x509v3' ]
     unless $ssl_lib =~ /WolfSSL/ or $openssl_ver ge "1.0.2";
 
+  $skip{'main/func_kdf.combinations'} = [ $ssl_lib =~ /OpenSSL 1\.0\./ ? 'new' : 'old' ];
+
   $skip{'main/ssl_verify_ip.test'} = 'x509v3 support required'
     unless $openssl_ver ge "1.0.2";