userspace_kill: only sleep 1 second on failure
userspace_kill: only sleep 1 second on failure

10 seconds may be too long, and 1 message / sec is
okay in terms of log spam.

I decided to NOT use a #define for the value, because
then several literal strings would have to be replaced
with snprintf. Not worth it.

https://github.com/rfjakob/earlyoom/issues/74

rfjakob/earlyoom,rfjakob/earlyoom,rfjakob/earlyoom,rfjakob/earlyoom