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
Generate alphanumerical random strings.
Prior this change curl used to create random hex strings. This was
mostly okay, but having alphanumerical random strings is better: The
strings have more entropy in the same space.
The MIME multipart boundary used to be mere 64-bits of randomness due
to being 16 hex chars. With these changes the boundary is 22
alphanumerical chars, or little over 130 bits of randomness.
Closes#11838
