[#1539] More user friendly message when generating SSH key without a comment.

Problem description
===============
The message that is displayed when generating a SSH key without a comment should be more user friendly.

Changes description
===============
A new message will be added if no comment is specified for the SSH key in the command line options.

How to try and test the changes
========================
reviewers @adiroiban @alibotean @lgheorghiu

Run

paver deps
paver build
cd build-*/
cd bin # For Unix.

When running, and no comment is specified :
$ ./server-commands.sh --generate-key

"without a comment" string should be present at the end of the message.

SSH key of type "rsa" and length "1024" generated as public key file "id_rsa.pub" and private key file "id_rsa" without a comment.