Gzip openstack service logs

These files are quite large and disk space is limited so make sure we
compress the log files before copying them to storage. Additionally
os-loganalyze will only operate on gzipped log files so this should fix
os-loganalyze with tempest-full job's logs.

This is mostly a check to confirm everything works as expected but we
probably want to move the gzip step into the log publication roles so
that all log files end up compressed.

Change-Id: Ie87962428e0ca755c211cc5e664a14a9f2a79ac4

roles/export-devstack-journal/tasks/main.yaml

@@ -15,7 +15,7 @@
       name=""
       for u in `systemctl list-unit-files | grep devstack | awk '{print $1}'`; do
         name=$(echo $u | sed 's/devstack@/screen-/' | sed 's/\.service//')
-        journalctl -o short-precise --unit $u | tee {{ stage_dir }}/logs/$name.txt > /dev/null
+        journalctl -o short-precise --unit $u | gzip - > {{ stage_dir }}/logs/$name.txt.gz
       done
 
       # Export the journal in export format to make it downloadable
@@ -34,4 +34,4 @@
           -t sudo \
           --no-pager \
           --since="$(cat {{ devstack_base_dir }}/log-start-timestamp.txt)" \
-        | tee {{ stage_dir }}/logs/syslog.txt > /dev/null
+        | gzip - > {{ stage_dir }}/logs/syslog.txt.gz