It is hard to grep errors in current log. so in this patch,
I'm updating die function which also writes log for
screen_log_dir/error.log.
In future, we may categolize negative fault by using
this error.log.
Change-Id: I70a8cfe67ed408284f5c88c762c6bb8acb8ecdb2
from time to time horizon gets broken in devstack and it
takes a while to figure out why. Put a sanity check into
devstack exercises that checks for horizon front page being
up and not just a stack trace to use as a simple gate.
Change-Id: I13a6c59881f618d5194b1625b67115013c9cb6c2