stage1: gpg verify and cache retrieved coreos image

Depends on the failure mode, but basically you see the output of gpg & curl, so if say dns fails the build looks like:
Generating and packaging rootfs (stage1)...
~/rocket/rocket/stage1 ~/rocket/rocket
gpg: no signed data
gpg: can't hash datafile: No data
curl: (6) Couldn't resolve host 'zzzstable.release.core-os.net'
$

Permissions problem on cache directory:
Building actool...
Building ACE validator...
Building init (stage1)...
Packaging init (stage1)...
Generating and packaging rootfs (stage1)...
~/rocket/rocket/stage1 ~/rocket/rocket
gpg: can't open `/home/vc/rocket/rocket/stage1/cache/pxe.img.sig': Permission denied
gpg: verify signatures failed: Permission denied
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0Warning: Failed to create the file 
Warning: /home/vc/rocket/rocket/stage1/cache/pxe.img: Permission denied
  0  108M    0   503    0     0    981      0 32:19:18 --:--:-- 32:19:18  1612
curl: (23) Failed writing body (0 != 503)
$