Session Management: Allow killing multiple specific sessions

The intent of this change is to allow the user to specify multiple sessions to kill when using the sessions -k switch.  This uses the `build_sessions_array` function added in PR #3401 which is now landed.

    sessions -k <session id range> 
    sessions -k 1,3,5-8

Here is an example that specifies a single session, a range, and an invalid session ID.

```
msf exploit(psexec) > sessions 

Active sessions
===============

  Id  Type                   Information                    Connection
  --  ----                   -----------                    ----------
  1   meterpreter x86/win32  NT AUTHORITY\SYSTEM @ WINDC01 192.168.180.102:8343 ->192.168.190.210:49526 (192.168.190.210)
  2   meterpreter x86/win32  NT AUTHORITY\SYSTEM @ WINDC01 192.168.180.102:8343 ->192.168.190.210:49528 (192.168.190.210)
  3   meterpreter x86/win32  NT AUTHORITY\SYSTEM @ WINDC01 192.168.180.102:8343 ->192.168.190.210:49529 (192.168.190.210)
  4   meterpreter x86/win32  NT AUTHORITY\SYSTEM @ WINDC01 192.168.180.102:8343 ->192.168.190.210:49530 (192.168.190.210)
  5   meterpreter x86/win32  NT AUTHORITY\SYSTEM @ WINDC01 192.168.180.102:8343 ->192.168.190.210:49532 (192.168.190.210)
  6   meterpreter x86/win32  NT AUTHORITY\SYSTEM @ WINDC01 192.168.180.102:8343 ->192.168.190.210:49533 (192.168.190.210)

msf exploit(psexec) > sessions -k 1,3-5,7
[*] Killing the following session(s): [1, 3, 4, 5, 7]
[*] Killing session 1
[*]192.168.190.210 - Meterpreter session 1 closed.
[*] Killing session 3
[*]192.168.190.210 - Meterpreter session 3 closed.
[*] Killing session 4
[*]192.168.190.210 - Meterpreter session 4 closed.
[*] Killing session 5
[*]192.168.190.210 - Meterpreter session 5 closed.
[-] Invalid session identifier: 7
msf exploit(psexec) > sessions 

Active sessions
===============

  Id  Type                   Information                    Connection
  --  ----                   -----------                    ----------
  2   meterpreter x86/win32  NT AUTHORITY\SYSTEM @ WINDC01 192.168.180.102:8343 ->192.168.190.210:49528 (192.168.190.210)
  6   meterpreter x86/win32  NT AUTHORITY\SYSTEM @ WINDC01 192.168.180.102:8343 ->192.168.190.210:49533 (192.168.190.210)
```
never mind, you are doing assignment here on purpose