ktest: Add back "tail -1" to kernelrelease make

ktest: Add back "tail -1" to kernelrelease make

Commit ec9eb727e227 "ktest: Use make -s kernelrelease" fixed commit
2da95fba3547 "kbuild: fake the "Entering directory ..." message more simply"
as that commit added output after the make kernelrelease. But there's still
some build scripts that are used by ktest that has output before the make
is executed, and requires that only the last line is printed.

Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>