Uve Code re-org
1. Removed UveClient class and defined separate classes to represent each of the UVEs (VM, VN and Vrouter UVE)
2. Follow other coding conventions (Convert naked pointers to smart pointers, .Follow one file, one class convention, Remove singletons etc.)
3. Moved test case of agent/uve/test_vn_vmlist.cc to agent/uve/test_vn_uve.cc. Removed file agent/uve/test_vn_vmlist.cc
4. Moved test cases agent/test/test_uve.cc and agent/test/test_stats_mock.cc to agent/uve/test