tests/keyctl: improve readability

tests/keyctl: improve readability

* tests/keyctl.c: Since do_keyctl() has so convoluted calling convention
and keyctl test is so complex, let's try to improve readability a bit
with some conventions regarding do_keyctl() call formatting: arguments
representing single keyctl argument should be put on the separate line,
continuations of arguments related to the same keyctl argument should
have additional indentation and termination 0UL should always be
on a separate line.  Also, while we are here, let's add spaces
to two type casts that are missing them.