If Pull() fails, which it does on registry or network flakes,
bail out early: there's no point in continuing. Same with
Save() and restoreImageFromCache(), although those are
unlikely to fail.
Possibly better solution: retry with backoff. Left as exercise
for future maintainer.
Use Expect() for failure checks, and correct two existing
instances of Printf()/Exit() to also use Expect().
Signed-off-by: Ed Santiago <santiago@redhat.com>
5f5bea0d12