Fix concurrency issue in XmppMessageBuilder

Do not access BgpPath from bgp::SendTask because the path can get
deleted from db::DBTable task which could be running in parallel.
Store vrf_originated_ attribute in RibOutAttr instead of accessing
the best path to figure out if the route is local Vrf Originated.

Change-Id: I47e45efa28ca51d68f1233c77606a2c499b0678c
Closes-Bug: 1402785