shill: wifi: Scan for hidden SSIDs

Find all services with the "hidden" property set.  If any exist,
specify the "SSIDs" argument to wpa_supplicant and supply up to
MAX_SSIDS-1 of them as arguments to the scan, as well as the
broadcast SSID.

Side effect -- removed the "services_" vector from the Service
superclass.  I don't think a non-subclassed Service vector makes
any sense to keep around.

BUG=chromium-os:22074
TEST=New Unit Test

Change-Id: I52af8b81d301a9561812af04a16df6e6fcc644bc
Reviewed-on: https://gerrit.chromium.org/gerrit/11347
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Commit-Ready: Paul Stewart <pstew@chromium.org>
Tested-by: Paul Stewart <pstew@chromium.org>
diff --git a/accessor_interface.h b/accessor_interface.h
index 7186a54..68b2837 100644
--- a/accessor_interface.h
+++ b/accessor_interface.h
@@ -63,6 +63,8 @@
   std::map<std::string, uint32> uint_property_;
 };
 
+typedef std::vector<uint8_t> ByteArray;
+typedef std::vector<ByteArray> ByteArrays;
 typedef std::vector<std::string> Strings;
 typedef std::map<std::string, std::string> Stringmap;
 typedef std::vector<Stringmap> Stringmaps;