Check for concurrent port binding deletion before binding the port

When agent tries to update port binding (DVR or regular), the port
might have already been deleted via API call.
This is not an error condition but should be handled to avoid traces
in the logs.

Change-Id: Ie9436172151f0ecd5b3e4667328910b09f8ef141
Closes-Bug: #1370570
Merge "Check for concurrent port binding deletion before binding the port"