Change TLS proto version on the test httpd server to test setting
combinations of --tls13-ciphers and --ciphers.
To not let the changed config of the httpd server bleed into the next
test, clean and reload on each test. Because a reload is slow, only
do this if the config is different than the loaded config. For this
the httpd.reload_if_config_changed() method is added.
Overloading of autouse fixtures does not seem to work. For the test
httpd server to be reloaded with a clean config in test_18_methods,
to not be affected by the config changes in test_17_ssl_use, the two
class scope fixtures of test_18_methods are now combined.
Closes#14589
