possible fix for delayshell indeterminism of dns timings

Noticed a discrepancy in dns timings dns timings were off sometimes a rtt.
Not entirely sure why this is, checked chrome dns queries and even in incognito chrome sometimes sends a deterministic bunch of dns queries too chromium-i18n.appspot.com and google.com,
 either by chromedrivier issuing the request due to url entering (prefetching google search results) or some google stuff to protect one from malware etc.
anyhow, timings should not never differ across runs.
i think its some request pipelining issue in replayshell passing --all-servers to dnsmasq seems to resolve this, allthough i have no idea why, which is kinda dangerous.

Observe Ticket: ravinet/mahimahi#105

Author: worenga

src/util/dns_server.cc

@@ -16,7 +16,9 @@ using namespace std;
 
 ChildProcess start_dnsmasq( const vector< string > & extra_arguments )
 {
-    vector< string > args = { DNSMASQ, "--keep-in-foreground", "--no-resolv",
+
+    vector< string > args = { DNSMASQ, "--keep-in-foreground", "--no-resolv", "--all-servers",
+//			      "--log-facility=-", "-q",  //comment this in to see dns queries in console
                               "--no-hosts",
                               "-C", "/dev/null" };