Capture all fstrm_capture output

The fstrm_capture.out file is overwritten when the fstrm_capture utility
is restarted during the "dnstap" system test.  Use a separate output
file for each fstrm_capture instance to ensure all output produced by
that tool during the "dnstap" system test is preserved for forensic
purposes.

(cherry picked from commit bd2941fc72)

bin/tests/system/dnstap/clean.sh

@@ -18,7 +18,7 @@ rm -f */named.run.prev
 rm -f */named.stats
 rm -f dig.out*
 rm -f dnstap.*
-rm -f fstrm_capture.out
+rm -f fstrm_capture.out.*
 rm -f ns*/dnstap.out
 rm -f ns*/dnstap.out.save
 rm -f ns*/dnstap.out.save.?

bin/tests/system/dnstap/tests.sh

@@ -79,7 +79,7 @@ mv ns2/dnstap.out ns2/dnstap.out.save
 
 if [ -n "$FSTRM_CAPTURE" ] ; then
 	$FSTRM_CAPTURE -t protobuf:dnstap.Dnstap -u ns4/dnstap.out \
-		-w dnstap.out > fstrm_capture.out 2>&1 &
+		-w dnstap.out > fstrm_capture.out.1 2>&1 &
 	fstrm_capture_pid=$!
 fi
 
@@ -674,7 +674,7 @@ EOF
 	mv dnstap.out dnstap.out.save
 
 	$FSTRM_CAPTURE -t protobuf:dnstap.Dnstap -u ns4/dnstap.out \
-		-w dnstap.out > fstrm_capture.out 2>&1 &
+		-w dnstap.out > fstrm_capture.out.2 2>&1 &
 	fstrm_capture_pid=$!
 	sleep 1
 	$RNDCCMD -s 10.53.0.4 dnstap -reopen | sed 's/^/ns4 /' | cat_i