Fix up the pack strings

While reviewing https://github.com/rapid7/metasploit-framework/pull/1018 I noticed some crazy appending going on with packed arrays.

The provided syntax is far easier to follow.

Can you please test this change in your environment and let me know if it's what you intended? I guessed a little on the types of some of the variables (I assume they all wanted to be Strings, or else your original wouldn't have worked at all).

Is there a module or something I can use to exercise the functionality? I assumed https://github.com/rapid7/metasploit-framework/pull/1028  was related, but nope. I'm just kind of stumped as to how to test this (any advice there would be appreciated).