Lab 6.3 suggested corrections

In Lab 6.3 we see:

student@ubuntu:~$ sudo rkt run docker://nginx registry-1.docker.io/library/busybox:latest --name=bzbx

This fails with:

kevincsmallwood@ubuntu:~$ sudo rkt run docker://nginx registry-1.docker.io/library/busybox:latest --name=bzbx
run: discovery failed

We first need to "fetch" the busybox image as in:

kevincsmallwood@ubuntu:~$ sudo rkt fetch --insecure-options=image docker://busybox:latestDownloading sha256:61c5ed1cbdf [===============================] 764 KB / 764 KB
sha512-a46026cbdd17a62f818269a47505f900

After the "fetch" operation, the "run" of the two images in one pod works okay.