Make User-Agent easier to control across modules and more consistent

[hdm]

Source http://blog.didierstevens.com/2015/03/16/quickpost-metasploit-user-agent-strings/

[Chiggins]

Not knowing much about the source and how options are handled, but what if Metasploit had one default User-Agent string and all modules used that, unless otherwise specified via set/setg?

[hdm]

That is mostly the case today, but some modules redefine the default, this ticket would be to clear those defaults and rely on a consistent option (such as the one the HttpClient mixin offers).

[OJ]

Could be fun to have a generator that generates UA strings so that each case is different :)

[pyrohaz4good]

@hmoore-r7 Didier's post is very must the exact reason for #4984 :-)

[wchen-r7]

Some modules don't really need to redefine the user-agent. But it looks like most of them are pretty old so it's kind of hard to find the vulnerable software and verify (especially the memory corruption ones).

[bcook-r7]

We added a common user agent list to meterpreter, closing.