worktree: teach "add" to ignore submodule.recurse config

worktree: teach "add" to ignore submodule.recurse config

"worktree add" internally calls "reset --hard", but if
submodule.recurse is set, reset tries to recurse into
initialized submodules, which makes start_command try to
cd into non-existing submodule paths and die.

Fix that by making sure that the call to reset in "worktree add"
does not recurse.

Signed-off-by: Philippe Blain <levraiphilippeblain@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>