modules/system/upstart-events/shutdown.nix: refer to bash binary with full path
modules/system/upstart-events/shutdown.nix: refer to bash binary with full path

Upstart won't find a "bash" binary in $PATH when those commands are run, so we
refer to it using an absolute path.

git-svn-id: 71c8032c709790ec749031c4215f8515ac00dc5a@31157 70bd8c7a-acb8-0310-9f0d-9cc1c95dcdbb

bnordgren/nixos,bnordgren/nixos,bnordgren/nixos,bnordgren/nixos,bnordgren/nixos