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_engine.gyp b/update_engine.gyp
index 7a3be60..880a03a 100644
--- a/update_engine.gyp
+++ b/update_engine.gyp
@@ -252,6 +252,7 @@
         'boot_control_chromeos.cc',
         'common_service.cc',
         'connection_manager.cc',
+        'connection_utils.cc',
         'daemon.cc',
         'dbus_service.cc',
         'hardware_chromeos.cc',