shill: fix test failures in WiFiRoaming.005Suspend* tests

- update PowerManagerProxy to reflect the new path used
  by /usr/bin/powerd_suspend
  (see https://gerrit.chromium.org/gerrit/17161)
- flush wpa_supplicant's BSS cache on resume

TEST=WiFiRoaming.005Suspend*, unit tests
BUG=chromium-os:27394,chromium-os:27474,chromium-os:27473

Change-Id: I49166137a48f928121ce387c82b6e01948505405
Reviewed-on: https://gerrit.chromium.org/gerrit/17744
Commit-Ready: mukesh agrawal <quiche@chromium.org>
Reviewed-by: mukesh agrawal <quiche@chromium.org>
Tested-by: mukesh agrawal <quiche@chromium.org>
diff --git a/power_manager_proxy.cc b/power_manager_proxy.cc
index 7d07c67..2531e15 100644
--- a/power_manager_proxy.cc
+++ b/power_manager_proxy.cc
@@ -10,7 +10,6 @@
 using std::string;
 
 namespace shill {
-const char PowerManagerProxy::kRootPath[] = "/";
 
 PowerManagerProxy::PowerManagerProxy(PowerManagerProxyDelegate *delegate,
                                      DBus::Connection *connection)
@@ -25,12 +24,13 @@
 PowerManagerProxy::Proxy::Proxy(PowerManagerProxyDelegate *delegate,
                                 DBus::Connection *connection)
     : DBus::ObjectProxy(*connection,
-                        kRootPath,
+                        power_manager::kPowerManagerServicePath,
                         power_manager::kPowerManagerServiceName),
       delegate_(delegate) {}
 
 PowerManagerProxy::Proxy::~Proxy() {}
 
+// TODO(quiche): make this signal work again. crosbug.com/27475
 void PowerManagerProxy::Proxy::SuspendDelay(const uint32_t &sequence_number) {
   VLOG(2) << __func__ << "(" << sequence_number << ")";
   delegate_->OnSuspendDelay(sequence_number);