kernel/selinux-testsuite: abort the test when infra fails
    
    CKI interprets the "Abort" result as an infra failure and waives the
    test in such case. So if "git clone" fails, it's better to abort the
    whole test so that a false positive test failure is not reported.
    
    Turns out that Beaker interprets the exit code 127 (possibly other ones,
    but this one I'm sure about) as Abort, so we can just do that instead of
    relying on the legacy rhts-abort command.
    
    Signed-off-by: Ondrej Mosnacek <omosnace@redhat.com>