Keep the Usage of exit()/sys.exit() Consistent

It's better to keep the usage of exit()/sys.exit() consistent
in one file. Furthermore, sys.exit() is considered good to be
used in production code, while exit is for interactive shell.

Change-Id: Ia3092853a648922588e2bc11db37d6decdec1b48

bin/swift-oldies

@@ -59,7 +59,7 @@ Lists old Swift processes.
             listing.append((str(hours), pid, args))
 
     if not listing:
-        exit()
+        sys.exit()
 
     hours_len = len('Hours')
     pid_len = len('PID')

bin/swift-orphans

@@ -93,7 +93,7 @@ Example (sends SIGTERM to all orphaned Swift processes older than two hours):
             listing.append((str(hours), pid, args))
 
     if not listing:
-        exit()
+        sys.exit()
 
     hours_len = len('Hours')
     pid_len = len('PID')