lava_wait_jobs.py: Factor out function to fetch artifacts for single job

Intention is to parallelize waiting for job completion and fetching
artifacts (i.e. as soon as a complete job is detected, fetch artifacts
for it, instead of spending time waiting for other jobs to complete
first).

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I51d7cd1b3132bd25d25c893ff436dc18b197f074
1 file changed