Currently we only export the devstack@ services, and then separately
export the kernel & sudo logs to syslog.txt.
This leaves a lot of logs potentially behind in the journal for
various daemons. Just export the whole lot.
Using this output is currently very opaque and makes use of systemd
export tools that are very un-discoverable. Add a README that will
appear alongside the journal explaining how to actually use it. This
is a template as it would be nice to put into things like the list of
services that are in the journal, or maybe other magic.
Also make sure we export the logs since the start timestamp; currently
during a full run we drop the initial logs.
Change-Id: Id2626f9113d82c6d524039acda8a8ec74afb2081