Upgrade encryption of sensitive properties

Currently, NiFi accepts a password and encryption algorithm in nifi.properties which are used to encrypt all sensitive processor properties throughout the application. The password defaults to empty and the algorithm defaults to PBEWITHMD5AND256BITAES-CBC-OPENSSL. This algorithm:

• uses a digest function (MD5) which is not cryptographically secure [1][2][3][4]
• uses a single iteration count [5][6]
• limits password input to 16 characters on JVMs without the unlimited strength cryptographic jurisdiction policy files installed NIFI-1255

all of which combine to make it extremely insecure. We should change the default algorithm to use a strong key derivation function (KDF) [7] which will properly derive a key to protect the sensitive properties.

Because existing systems have already encrypted the properties using a key derived from the original settings, we should provide a translation/upgrade utility to seamlessly convert the stored values from the old password & algorithm combination to the new.

[1] http://security.stackexchange.com/a/19908/16485
[2] http://security.stackexchange.com/a/31846/16485
[3] http://security.stackexchange.com/questions/52461/how-weak-is-md5-as-a-password-hashing-function
[4] http://security.stackexchange.com/a/31410/16485
[5] http://security.stackexchange.com/a/29139/16485
[6] https://www.openssl.org/docs/manmaster/crypto/EVP_BytesToKey.html
[7] https://cwiki.apache.org/confluence/display/NIFI/Key+Derivation+Function+Explanations