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/update_manager/device_policy_provider.h b/update_manager/device_policy_provider.h
index 0eb04c1..3537d13 100644
--- a/update_manager/device_policy_provider.h
+++ b/update_manager/device_policy_provider.h
@@ -52,7 +52,7 @@
   // Variable returning the set of connection types allowed for updates. The
   // identifiers returned are consistent with the ones returned by the
   // ShillProvider.
-  virtual Variable<std::set<ConnectionType>>*
+  virtual Variable<std::set<chromeos_update_engine::ConnectionType>>*
       var_allowed_connection_types_for_update() = 0;
 
   // Variable stating the name of the device owner. For enterprise enrolled