this commit adds a fairly generic mechanism for passing extra
params into the ISO post command when scheduling jobs, and an
arg to the compose sub-command which takes advantage of this
to let you specify an updates image URL which will cause the
new GRUBADD var to be specified when POSTing the jobs, thus
loading that updates image for all the tests. This should give
us a handy way to run a full openQA test run on any updates
image we like.
When extra parameters are specified, the BUILD value is changed
so this test run can be identified as not being a 'pure' one.
get_passed_testcases is tweaked to make sure we never report
results to the wiki for such tests.
This goes with D801 for the tests.