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
It is still possible to override the executable to run during the test,
using the <tool> tag, but this patch removes the requirement that the
tag must be present for unit tests.
It also removes the possibility of human error when existing test cases
are used as the basis for new tests, as recently witnessed in 81c37124.
Reviewed-by: Daniel Stenberg
Closes#4976
