KVM: selftests: Reword the NX hugepage test's skip message to be more helpful

Rework the NX hugepage test's skip message regarding the magic token to
provide all of the necessary magic, and to very explicitly recommended
using the wrapper shell script.

Opportunistically remove an overzealous newline; splitting the
recommendation message across two lines of ~45 characters makes it much
harder to read than running out a single line to 98 characters.

Link: https://lore.kernel.org/r/20231129224042.530798-1-seanjc@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>