Accept either 2 or 3 old versions of log file

Depending upon when the directory is sampled there may be 2
(oldest version removed and rename / reopen is in progresss) or
3 old versions of the log file.

bin/tests/system/logfileconfig/tests.sh

@@ -196,11 +196,11 @@ _found2() (
 
         # we are configured to keep three versions, so the oldest
         # timestamped versions should be gone, and there should
-        # be two new ones.
+        # be two or three backup ones.
         [ -f ns1/named_ts.1480039317 ] && return 1
         [ -f ns1/named_ts.20150101120000120 ] && return 1
         set -- ns1/named_ts.*
-        [ "$#" -eq 2 ] || return 1
+        [ "$#" -eq 2 -o "$#" -eq 3 ] || return 1
 )
 retry_quiet 5 _found2 || ret=1
 if [ "$ret" -ne 0 ]; then echo_i "failed"; fi