Partial-Bug: 1464016 Handle route-target updates cleanly
Partial-Bug: 1464016 Handle route-target updates cleanly

Keep number of route-targets at least 1 all the time. This ensures that the
routing-instance need not be created/deleted when first target is applied or
all targets go away and makes the management logic simple. We have separate
events for routing-instance creation and deletion anyways

Change-Id: I06a1ccabb697b2f2ddd329bf2313239a6a119f4f

numansiddique/contrail-controller,nischalsheth/contrail-controller,eonpatapon/contrail-controller,tcpcloud/contrail-controller,numansiddique/contrail-controller,sajuptpm/contrail-controller,reiaaoyama/contrail-controller,sajuptpm/contrail-controller,eonpatapon/contrail-controller,sajuptpm/contrail-controller,rombie/contrail-controller,vpramo/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,tcpcloud/contrail-controller,rombie/contrail-controller,facetothefate/contrail-controller,reiaaoyama/contrail-controller,DreamLab/contrail-controller,nischalsheth/contrail-controller,codilime/contrail-controller,nischalsheth/contrail-controller,vmahuli/contrail-controller,vmahuli/contrail-controller,facetothefate/contrail-controller,eonpatapon/contrail-controller,hthompson6/contrail-controller,DreamLab/contrail-controller,nischalsheth/contrail-controller,tcpcloud/contrail-controller,codilime/contrail-controller,rombie/contrail-controller,numansiddique/contrail-controller,vpramo/contrail-controller,sajuptpm/contrail-controller,nischalsheth/contrail-controller,vmahuli/contrail-controller,sajuptpm/contrail-controller,rombie/contrail-controller,numansiddique/contrail-controller,DreamLab/contrail-controller,facetothefate/contrail-controller,nischalsheth/contrail-controller,codilime/contrail-controller,vpramo/contrail-controller,hthompson6/contrail-controller,reiaaoyama/contrail-controller,vpramo/contrail-controller,reiaaoyama/contrail-controller,hthompson6/contrail-controller,vpramo/contrail-controller,hthompson6/contrail-controller,rombie/contrail-controller,sajuptpm/contrail-controller,eonpatapon/contrail-controller,DreamLab/contrail-controller,nischalsheth/contrail-controller,facetothefate/contrail-controller,vmahuli/contrail-controller,tcpcloud/contrail-controller,nischalsheth/contrail-controller,DreamLab/contrail-controller,tcpcloud/contrail-controller,hthompson6/contrail-controller,vmahuli/contrail-controller,numansiddique/contrail-controller,facetothefate/contrail-controller,codilime/contrail-controller,eonpatapon/contrail-controller,rombie/contrail-controller,codilime/contrail-controller,reiaaoyama/contrail-controller,tcpcloud/contrail-controller,eonpatapon/contrail-controller,codilime/contrail-controller