generic/228: fix restoration of kernel.core_pattern sysctl

generic/228 changes kernel.core_pattern, so it saves it beforehand in
order to restore it. However, it adds an extra space in the process:

$ echo \"$(sysctl kernel.core_pattern | awk -F = '{print $NF}')\"
" |/usr/lib/systemd/systemd-coredump %P %u %g %s %t %c %h %e"

Instead of using awk, just use sysctl -n to only print the value.

Signed-off-by: Omar Sandoval <osandov@fb.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

tests/generic/228

@@ -45,7 +45,7 @@ avail=`df -P $TEST_DIR | awk 'END {print $4}'`
 [ "$avail" -ge 104000 ] || _notrun "Test device is too small ($avail KiB)"
 
 # Suppress core dumped messages
-core_pattern=`sysctl kernel.core_pattern | awk -F = '{print $NF}'`
+core_pattern=`sysctl -n kernel.core_pattern`
 ulimit_c=`ulimit -c`
 sysctl -w kernel.core_pattern=core &>/dev/null
 ulimit -c 0