[v9_11] Make "kyua report-html" less verbose on stdout
kyua report-html command in CI generates more than two pages of output
to stdout, which is nothing but which HTML pages Kyua generated, e.g.:
Generating kyua_html/context.html Generating kyua_html/lib_dns_tests_acl_test_main.html ... Generating kyua_html/lib_ns_tests_query_test_main.html Generating kyua_html/report.css Generating kyua_html/index.html
This is seldomly useful and requires the user to scroll three pages upwards to get to unit test results.
(cherry picked from commit 74fa1962)