client: lib_docker: exec: only allocate pseudo-TTY when needed

client/src/docker/lib/internal/lib_docker.bash

@@ -507,7 +507,9 @@ function lib_docker::__shell()
 
 function lib_docker::__exec()
 {
-  docker exec -it "$global_container" /bin/bash -i -c "$@"
+  local _tty
+  test -t 1 && _tty="t"
+  docker exec -i"$_tty" "$global_container" /bin/bash -i -c "$@"
 }
 
 function lib_docker::__parse_args_edit()