'uname -o' is not portable, suppress error message; remove spurious cat tmp.out; provide forensics for failure analysis

bin/tests/system/metadata/clean.sh

@@ -12,4 +12,5 @@ rm -f pending.key rolling.key standby.key inact.key
 rm -f prerev.key postrev.key oldstyle.key
 rm -f keys sigs
 rm -f tmp.out
+rm -f settime1.test* settime2.test*
 rm -f ns*/named.lock