testsuite: choose a random loopback IP address to work on

testsuite

@@ -17,7 +17,7 @@
 #             if it already exists, it will not be cleaned up.
 #  -  TESTIP: the IP address to use for testing.
 #             the user needs to be able to open listening sockets, and to connect to them
-#             by default, 127.7.8.9
+#             by default, choose a random IP in 127.0.0.0/8
 
 # Author: Daniel Kahn Gillmor <dkg@fifthhorseman.net>
 # 2018-08-29
@@ -41,7 +41,7 @@ if [ -z "$WORKDIR" ]; then
 else
     d="$WORKDIR"
 fi
-ip="${TESTIP:-127.7.8.9}"
+ip="${TESTIP:-127.$(( $RANDOM % 256 )).$(( $RANDOM % 256 )).$(( $RANDOM % 256 ))}"
 
 printf "hddemux test\n------------\n  binary: %s\n workdir: %s\n IP addr: %s\n" "$hddemux" "$d" "$ip"