autotest: Add simple test to verify operation of dual radio router

This will assist us in bringing up multi-radio routers quickly.

TEST=suite wifi_matfunc passes with these changes to
site_linux_system.py
BUG=chromium:313963
Change-Id: Id4fa86b9df0d3ba68c9fed2e546e894ddd84aee0
Reviewed-on: https://chromium-review.googlesource.com/176117
Tested-by: Christopher Wiley <wiley@chromium.org>
Reviewed-by: Paul Stewart <pstew@chromium.org>
Commit-Queue: Christopher Wiley <wiley@chromium.org>
diff --git a/server/site_linux_router.py b/server/site_linux_router.py
index cd30f40..779497c 100644
--- a/server/site_linux_router.py
+++ b/server/site_linux_router.py
@@ -225,6 +225,7 @@
                 log_file, pid_file, conf_file)
         self.router.run(start_command)
         self.hostapd_instances.append({
+            'ssid': conf['ssid'],
             'conf_file': conf_file,
             'log_file': log_file,
             'interface': interface,
@@ -758,10 +759,10 @@
         self.router.run('grep -q "%s" %s' % (pmksa_match, instance['log_file']))
 
 
-    def get_ssid(self):
+    def get_ssid(self, instance=0):
         """@return string ssid for the network stemming from this router."""
-        if self.hostapd['configured']:
-            return self.hostapd['conf']['ssid']
+        if self.hostapd_instances:
+            return self.hostapd_instances[instance]['ssid']
 
         if not 'ssid' in self.station['conf']:
             raise error.TestFail('Requested ssid of an unconfigured AP.')