zuul: use lowercase connection names and canonical_hostname

...because this string is what Zuul uses when mapping from Depends-on
commit tags to connections, and because Python's urllib for some reason
decided to return a *lowercase* version of URL hostnames. And because
CzechLight != czechlight, arrrrrgh.

Change-Id: I3fd4205c1010b400b7a53d1457eb76309afcaf62
diff --git a/files/zuul/zuul.conf b/files/zuul/zuul.conf
index 0caa835..20e7bf1 100644
--- a/files/zuul/zuul.conf
+++ b/files/zuul/zuul.conf
@@ -44,10 +44,10 @@
 sshkey = /var/lib/zuul/.ssh/id_rsa
 user = cesnet-zuul-public
 
-[connection cesnet-gerrit-CzechLight]
+[connection cesnet-gerrit-czechlight]
 driver = gerrit
 server = gerrit.cesnet.cz
-canonical_hostname = cesnet-gerrit-CzechLight
+canonical_hostname = cesnet-gerrit-czechlight
 gitweb_url_template = {baseurl}/plugins/gitiles/{project.name}/+/{sha}^!/
 sshkey = /var/lib/zuul/.ssh/id_rsa
 user = cesnet-zuul-czechlight