Move ParseConnection*() to connection_utils.

We don't need real_shill_provider if USE_DBUS is 0, but we still need
these functions, and they have a duplicate copy in connection_manager,
so put them in utils and deduplicate.

Also moved StringForConnectionType() to connection_utils.

Bug: 28800946
Test: mma

Change-Id: If535fdc52bc8fb267921bea02b31d8d6580d5d54
diff --git a/payload_state.cc b/payload_state.cc
index af1ad05..1da472f 100644
--- a/payload_state.cc
+++ b/payload_state.cc
@@ -31,6 +31,7 @@
 #include "update_engine/common/hardware_interface.h"
 #include "update_engine/common/prefs.h"
 #include "update_engine/common/utils.h"
+#include "update_engine/connection_manager_interface.h"
 #include "update_engine/metrics_utils.h"
 #include "update_engine/omaha_request_params.h"
 #include "update_engine/payload_consumer/install_plan.h"
@@ -186,8 +187,8 @@
   attempt_num_bytes_downloaded_ = 0;
 
   metrics::ConnectionType type;
-  NetworkConnectionType network_connection_type;
-  NetworkTethering tethering;
+  ConnectionType network_connection_type;
+  ConnectionTethering tethering;
   ConnectionManagerInterface* connection_manager =
       system_state_->connection_manager();
   if (!connection_manager->GetConnectionProperties(&network_connection_type,