web: Rename test-channel.html to test-chan.html

The way automake testing works is that each test generates a log file
with the same filename as the extension and .log. So multiple tests
with different extensions but the same name will generate the same
log file, and only one will be run.

Renaming test-channel.html allows it to run again.

Closes #323
Reviewed-by: Marius Vollmer <marius.vollmer@redhat.com>