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

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

Commit 52d21580b362 "ktest: Use make -s kernelrelease" fixed commit
7ff525712acf "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>