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/common_service.cc b/common_service.cc
index ade5349..e284a93 100644
--- a/common_service.cc
+++ b/common_service.cc
@@ -273,9 +273,8 @@
   // Return the current setting based on the same logic used while checking for
   // updates. A log message could be printed as the result of this test.
   LOG(INFO) << "Checking if updates over cellular networks are allowed:";
-  *out_allowed = cm->IsUpdateAllowedOver(
-      chromeos_update_engine::NetworkConnectionType::kCellular,
-      chromeos_update_engine::NetworkTethering::kUnknown);
+  *out_allowed = cm->IsUpdateAllowedOver(ConnectionType::kCellular,
+                                         ConnectionTethering::kUnknown);
   return true;
 }