Fix Scons to allow UT run for pkt dir only
Fix Scons to allow UT run for pkt dir only

- Fixing scons script to add only pkt test-cases under
  pkt scons alias and add all under agent scons alias

Closes-Bug: 1571400
Change-Id: Ic977b04b15455eeb200cf4f3d377267ccae44411

tcpcloud/contrail-controller,tcpcloud/contrail-controller,tcpcloud/contrail-controller,tcpcloud/contrail-controller,tcpcloud/contrail-controller,tcpcloud/contrail-controller