Check responsiveness of http/3 server when running.
Also, a test case with http/2 or http/3 server requirement
now implicitly drags in a 'http' server and we need no longer
mention that in testdata.
Closes#15058
The threee tags `<name>`, `</name>` and `<command>` were frequently used
with a leading space that this removes. The reason this habbit is so
widespread in testcases is probably that they have been copy and pasted.
Hence, fixing them all now might curb this practice from now on.
Closes#12028
