RFC: avocado: Simplify human output messages

We can aim for a more terse output than what we have
today. This is my proposal to simplify things a bit,
while still being clear (I hope).

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>
avocado: Rename job output dir

We used 'run' as a prefix for avocado job output directories
after virt-test (basically, inertia). Let's use something
better:

job-[first 8 characters of job id]-timestamp

This way the job id starts to be more prominent in the
human interface as well.

Signed-off-by: Lucas Meneghel Rodrigues <lmr@redhat.com>