Test suite: If holding supported, add a new print job for cancelling

[zdohnal]

On some quicker machines the print-job operation finishes quicker than
we can cancel it in the test - so add job-hold-until job template
attribute if the printer supports it, which will hold the job until it
is cancelled by the next test.

The next test passes because it has both statuses (correct and error one)
as expected, but cupsd generates an additional error in log if the job
cancelling fails, which would be more dirty to cover in run-stp-test.sh.

There is a loophole when the error is still generated - if the printer/machine
is quick enough to finish the job, but the machine/printer doesn't support job
holding at the same time. IMHO the current patch should cover most cases.

Fixes? #155

[zdohnal]

@shirelyhhdl @sp1ritCS please test it and let me know whether it helps.

[michaelrsweet]

The only problem with this change is that the "ipp-1.1.test" file is also meant to test real printers, many of which will not support job-hold-until. So the use of job-hold-until should be made conditional on whether job-hold-until is supported.

[zdohnal]

@michaelrsweet I haven't found out how to make a specific attribute optional, so I've added a new print job with job-hold-until if the printer supports it, and adjusted requests count in run-stp-tests.sh accordingly.

[sp1ritCS]

I don't know how soon I'm able to test it, but I'll try

[zdohnal]

@sp1ritCS @shirelyhhdl any updates?

@michaelrsweet WDYT about the changes?