boxes: Return in bash is only allowed in functions

I was trying out the new base box scripts on a Debian sid+experimental system with LXC 1.0.0. When I try to `vagrant up` a machine, `lxc-create` fails due to an error in the LXC template:

    DEBUG driver: Creating container...
    INFO subprocess: Starting process: ["/usr/bin/sudo", "lxc-create", "--template", "vagrant-tmp-infra_git_1394543261259_54013", "--name", "infra_git_1394543261259_54013", "--", "--tarball", "/home/fpletz/.vagrant.d/boxes/precise-amd64/lxc/rootfs.tar.gz", "--config", "/home/fpletz/.vagrant.d/boxes/precise-amd64/lxc/lxc-config"]
    DEBUG subprocess: Selecting on IO
    DEBUG subprocess: stdout: Unpacking the rootfs
    DEBUG subprocess: stderr: /usr/share/lxc/templates/lxc-vagrant-tmp-infra_git_1394543261259_54013: line 124: return: can only `return' from a function or sourced script
    DEBUG subprocess: stderr: lxc_container: container creation template for infra_git_1394543261259_54013 failed
    DEBUG subprocess: stderr: lxc_container: Error creating container infra_git_1394543261259_54013

I'm running bash 4.3-2 on the host.The base box is an Ubuntu precise.

This patch replaces the return with exits. This is probably the behaviour that was intended. :smile: