manage jobs: allow to force fail a job
manage jobs: allow to force fail a job

This should only be used when something went wrong (for instance if lava-logs
was not able to parse the lava.job result) because the corresponding lava-run
process will *not* be killed.

Change-Id: I48144fc48fdbcd16b61be2308936da04686dd8f4

Linaro/lava-server,Linaro/lava-server,Linaro/lava-server,Linaro/lava-server