Add kerberos password property to NiFi HortonworksSchemaRegistry

In addition to the principal/keytab and KerberosCredentialsService options for accessing kerberized Schema Registry from the HortonworksSchemaRegistry controller service, a password field should be added.

Components should validate that only one set of options should be configured:

• principal and keytab
• principal and password
• KerberosCredentialsService