[VOL-1588] Improve Flow Add performance

This update consists of the following:
1) Update the performance when adding a flow to a logical device,
decomposing the flow into parent and child device and sending the
flow to the adapters.
2) Format a number of files as per GO fmt.
3) Ensure the device graph cache gets updated when a new port is
added to the graph that belongs to an existing device in cache.

The flow update/deletion performance will be addressed in a separate
commit.

Change-Id: I2eb663cc73eef9fc6172203ed88a35726f5fe008
diff --git a/rw_core/coreIf/logical_device_agent_if.go b/rw_core/coreIf/logical_device_agent_if.go
index 8394fac..c2614b2 100644
--- a/rw_core/coreIf/logical_device_agent_if.go
+++ b/rw_core/coreIf/logical_device_agent_if.go
@@ -20,9 +20,9 @@
 package coreIf
 
 import (
-	"github.com/opencord/voltha-protos/go/voltha"
 	"github.com/opencord/voltha-go/rw_core/graph"
 	"github.com/opencord/voltha-go/rw_core/utils"
+	"github.com/opencord/voltha-protos/go/voltha"
 )
 
 // LogicalAgent represents a generic agent