Add trailing slash for log url

Both on logs.o.o and vexxhost swift object-storage, without a trailing
slash, a request will get 301 to new location with trailing slash. By
adding a trailing slash here, and since this is usually a directory, we
can avoid a 301 redirect for browsers.

Note, zuul_return for zuul upload-logs and upload-logs-swift does
include trailing slash.

Change-Id: Ie58f3922680806a5c1865a44bb379ef66e2992fd
Signed-off-by: Paul Belanger <pabelanger@redhat.com>

roles/emit-job-header/tasks/main.yaml

@@ -17,7 +17,7 @@
           Triggered by: {{ zuul.change_url }}
           {% endif %}
           {% if zuul_log_url is defined and zuul_log_path is defined %}
-          Log URL (when completed): {{ zuul_log_url }}/{{ zuul_log_path }}
+          Log URL (when completed): {{ zuul_log_url }}/{{ zuul_log_path }}/
           {% endif %}
 
     - name: Print node information