Make acquire modules OS aware

[DissectBot]

Design requirements:

• Collection should be done for the whole set of os levels (e.g. Linux & fortigate incase of collection for a fortigate machine). The set of levels could be determined by looking at the (super) classes of OSPlugin for the specific target at hand.
• This determining of the set of OS levels is best implemented in dissect.target to have a single interface for this type of information. Take a sneak peek at how to replace the current system of determining OSes (linux, windows, mac, unknown) with this interface.
• A Module should be able to service multiple OSes. This means the SPECS etc. in a Module subclass should be devided based on OS.