Land rapid7#7178, Add a method to check the Powershell version

Author: pbarry-r7

lib/msf/core/post/windows/powershell.rb

@@ -30,6 +30,31 @@ def have_powershell?
     return false
   end
 
+  #
+  # Returns the Powershell version
+  #
+  def get_powershell_version
+    return nil unless have_powershell?
+
+    process, pid, c = execute_script('$PSVersionTable.PSVersion')
+
+    o = ''
+
+    while (d = process.channel.read)
+      if d == ""
+        if (Time.now.to_i - start < time_out) && (o == '')
+          sleep 0.1
+        else
+          break
+        end
+      else
+        o << d
+      end
+    end
+
+    o.scan(/[\d \-]+/).last.split[0,2] * '.'
+  end
+
   #
   # Get/compare list of current PS processes - nested execution can spawn many children
   # doing checks before and after execution allows us to kill more children...