shill: tweak logging

1. Output "Sorted service list" header once, instead of once
   per item in the list.
2. Change phrasing "Initiating connect" to "Requesting autoconnect".
   Previous phrasing was misleading, because it suggested an immediate
   action.
3. Log when WiFiService skips an autoconnect request. (Goes with
   change #2, to make it clear when an autoconnect does not take
   effect.)

BUG=None
TEST=manual

manual testing: ran some unit tests which exercised the log
statements, verified that the appropriate statements showed
in the log output.

Change-Id: I40df3a3a905ff522bbd4d0ab013b7df4051a6602
Reviewed-on: https://gerrit.chromium.org/gerrit/14089
Tested-by: mukesh agrawal <quiche@chromium.org>
Reviewed-by: Thieu Le <thieule@chromium.org>
Commit-Ready: mukesh agrawal <quiche@chromium.org>
diff --git a/wifi_service.cc b/wifi_service.cc
index ca55a06..a676fa2 100644
--- a/wifi_service.cc
+++ b/wifi_service.cc
@@ -121,6 +121,8 @@
     //    useless work (one AutoConnect per Service), which blocks
     //    more timely work.
     ConnectTask();
+  } else {
+    LOG(INFO) << "Suppressed autoconnect to " << friendly_name();
   }
 }