use encrypted passwords for the call home feature

The call home feature has global and per-device user name with multiple passwords.
The passwords in particular are plain text and should be encrypted using the new
AAA service below.

The service to encrypt the credentials is here:
https://github.com/opendaylight/aaa/blob/master/aaa-encrypt-service/src/main/java/org/opendaylight/aaa/encrypt/AAAEncryptionService.java

The service is implemented here:
https://github.com/opendaylight/aaa/blob/master/aaa-encrypt-service/src/main/java/org/opendaylight/aaa/encrypt/AAAEncryptionServiceImpl.java

The call home code is still to be merged as of today at

https://git.opendaylight.org/gerrit/#/c/49253/8