Reduce risk of tests failing due to slow downloads

Recently large numbers of the daily tests have been failing due to the initial downloads of the nfs root timing out. Evaluation of the LAVA logs shows that downloads from images.apertis.org are sub 1MB/s early in the morning when these tests tend to run.

At least whilst further investigation is performed to determine the cause of this slowness, massively bump the timeout (3 --> 15 min) so that these tests will run rather than failing.

Signed-off-by: Martyn Welch martyn.welch@collabora.com