Do not overwrite out/root if it already exists

This gives the option for the user to link to an already-existing rootfs
there.
Add error() function that prints messages in scary red
Rename temporary resolv.conf to a more unique name
Add binfmt_misc rule to run qemu-arm-static

Current invokation of qemu would not work if the host system did not
already have a binfmt_misc rule to invoke it. Add a temporary rule every
time we need to run qemu to ensure this will work.
Use out/target/L4T instead of out/root as rootfs directory

This will be useful if we support other distros in the future (e.g. Arch
Linux).