Performance improvement for enum_ad_computers post module

Previously for each value we had to call the API to get a ppValue then a pValue then ValueLength and Value for each attribute (default 4) for each entry (number of computers found).

This causes a large number of packets to perform small memreads. 

Now I just pull down the raw structure for each entry and search for the attributes and values in one go. I have set the MAX_SEARCH to 0 to un-limit the default search.

I have removed the x86 restriction in anticipation of:
https://github.com/rapid7/metasploit-framework/pull/1463


I have also made it report hosts to the database by default which should give a very comprehensive list of domain computers...

These changes should make the module more viable in practice - usable on x86 and much quicker to retrieve.