openqa/worker: prepare to handle multiple tap worker classes
I'm going to try splitting the tap jobs across multiple worker
hosts. We have quite a lot of tap jobs, now, and I have seen
sometimes a situation where all non-tap jobs have been run and
the non-tap worker hosts are sitting idle, but the single tap
worker host has a long queue of tap jobs to get through.
We can't just put multiple hosts per instance into the tap
class, because then we might get a case where job A from a tap
group is run on one host and job B from a tap group is run on
a different host, and they can't communicate. It's actually
possible to set this up so it works, but it needs yet more
complex networking stuff I don't want to mess with. So instead
I'm just gonna split the tap job groups across two classes,
'tap' and 'tap2'. That way we can have one 'tap' worker host
and one 'tap2' worker host per instance and arch, and they will
each get about half the tap jobs.
Unfortunately since we only have one aarch64 worker for lab it
will still have to run all the jobs, but for all other cases we
do have at least two workers, so we can split the load.
Signed-off-by: Adam Williamson <awilliam@redhat.com>