Update module stance instead of appending to it

[wvu]

This is a redux of the fixes #9387 and #9822.

While this is the correct solution, I think it's okay to keep the other code for safety.

Note that either the module or one of its mixins will need to set the appropriate stance. This fix simply makes stance a binary, so inheritance and mixin order are especially important now.

msf5 exploit(multi/http/struts2_rest_xstream) > pry
[*] Starting Pry shell...
[*] You are in exploit/multi/http/struts2_rest_xstream

[1] pry(#<Msf::Modules::Exploit__Multi__Http__Struts2_rest_xstream::MetasploitModule>)> stance
=> "aggressive"
[2] pry(#<Msf::Modules::Exploit__Multi__Http__Struts2_rest_xstream::MetasploitModule>)> aggressive?
=> true
[3] pry(#<Msf::Modules::Exploit__Multi__Http__Struts2_rest_xstream::MetasploitModule>)> passive?
=> false
[4] pry(#<Msf::Modules::Exploit__Multi__Http__Struts2_rest_xstream::MetasploitModule>)>
msf5 exploit(multi/http/struts2_rest_xstream) > run

[!] You are binding to a loopback address by setting LHOST to 127.0.0.1. Did you want ReverseListenerBindAddress?
[*] Started reverse TCP double handler on 127.0.0.1:4444
[-] The connection was refused by the remote host (127.0.0.1:8080).
^C[*] Exploit completed, but no session was created.
msf5 exploit(multi/http/struts2_rest_xstream) >

Please note that the default behavior of update_info is to convert to an array and append to it.

metasploit-framework/lib/msf/core/module/module_info.rb

Lines 90 to 95 in 93638b7

	# If it's not an array, convert it to an array and merge the
	# two
	if (info[name].kind_of?(Array) == false)
	curr = info[name]
	info[name] = [ curr ]
	end

#11711

[wvu]

I'm nixing this, since while I think an aggressive exploit (even if it uses passive code) is always aggressive, it is useful to see the distinct qualities, and I've already written the code to account for that.