Beaglebone cleanup

Dependent on https://github.com/NickDaly/freedom-maker/pull/44. freedom-maker will install the kernel package so we don't need to install it here.

Avoid making extra copies of kernel files on /boot.

Install flash-kernel for beaglebone image and run during first-run. Removed the mount proc command before running flash-kernel -- /proc is already mounted during first-run.

Also fixed a quote mismatch in provide-source setup script.