selftests: fix condition in run_tests

The check if there are any files to install in case of no files
compares "X  " with "X" so never false.

Remove extra spaces. It may make sense to use make's $(if) function
here.

Signed-off-by: Yauheni Kaliuta <yauheni.kaliuta@redhat.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>