This provides reporting for base_selinux tests (see D699). To
do it properly we need to add another magic value for 'env':
$PAYLOAD$, which uses the image 'payload' (a fedfind term) as
the environment. This duplicates a bit of code from default_
install_cb; we should really drop that and instead make the
$FOO$ magic values work for all keys, to keep things consistent
and avoid duplication, but I'll do that as a separate diff.
Converting 'generic' to 'Server' means that we'll report
results from the nightly 'generic' boot.iso images in the Server
column, which is the best choice.

After doing a test run with D699 included, test report
submission and make sure the values look correct (or if you can
manage to get the test run on the current nightly validation event,
you can see if reporting actually works).