tools: shmsnoop, sofdsnoop handle keyboard interrupt (#2126)

Handle keyboard interrupt to avoid backtrace printed out when user
presses Ctrl-C. Other tools have been fixed recently. Let's fix these
remaining tools.
diff --git a/tools/sofdsnoop.py b/tools/sofdsnoop.py
index 8256481..f633107 100755
--- a/tools/sofdsnoop.py
+++ b/tools/sofdsnoop.py
@@ -342,4 +342,7 @@
 b["events"].open_perf_buffer(print_event, page_cnt=64)
 start_time = datetime.now()
 while not args.duration or datetime.now() - start_time < args.duration:
-    b.perf_buffer_poll(timeout=1000)
+    try:
+        b.perf_buffer_poll(timeout=1000)
+    except KeyboardInterrupt:
+        exit()