build: Sort distributekernel METALOG when using -DNO_ROOT

The metalog is produced by install -M, which is not inherently sorted.
This results in non-deterministic file ordering in kernel.txz. Order the
files in kernel.txz to support reproducible builds.

PR: 283214
Reviewed by: emaste

Signed-off-by: Pat Maddox <pat@patmaddox.com>